Timetable

The key dates were:

Overview

On 9 April 2015, the deadline for standing for the general election, there were 464 political parties registered with the Electoral Commission. Candidates who did not belong to a party were either labelled as an Independent or not labelled at all.

The Conservative Party and the Labour Party had been the two biggest parties since 1922, and had supplied all the UK's prime ministers since 1935. Opininion polls had predicted that the two parties would receive a combined total of anywhere between 65% and 75% of votes, and would receive anywhere between 80% and 85% of the seats;^[22][23] and that, as such, the leader of one of the two parties would become the Prime Minister after the election. The Liberal Democrats had been the third largest party in the UK for many years; but as described by various political commentators, other parties had risen relative to the Liberal Democrats since the 2010 election.^[24][25] In order to emphasise this, The Economist stated that "the familiar three-party system of the Tories, Labour, and the Lib Dems appears to be breaking down with the rise of UKIP, the Greens and the SNP." Ofcom ruled that the major parties in Great Britain were the Conservatives, Labour, the Liberal Democrats and UKIP, the SNP a major party in Scotland, and Plaid Cymru a major party in Wales.^[26] The BBC's guidelines were similar but removed UKIP from their list of major parties, and instead stated that UKIP should be given "appropriate levels of coverage in output to which the largest parties contribute and, on some occasions, similar levels of coverage".^[27][28] Seven parties (Conservative, Labour, Liberal Democrat, UKIP, SNP, PC and Green) participated in the election leadership debates.^[29] Northern Ireland's political parties were not included in any debates, despite the DUP, a party based in Northern Ireland, being the fourth largest party in the UK going into the election.

National

Several parties operate in specific regions only. The main national parties, standing in most seats across all of the country, are listed below in order of the number of seats that they contested:

• Conservative Party: The Conservative Party was the senior party in the 2010-15 coalition government, having won the most seats (306) at the 2010 election. The party stood in 647 seats (every seat except for two in Northern Ireland and the Speaker's seat).
• Labour Party: Labour had been in power from 1997 to 2010. The party was Her Majesty's Most Loyal Opposition after the 2010 election, having won 258 seats. It stood in 631 constituencies,^{[n 2]} missing only the Speaker's seat, and all seats in Northern Ireland.
• Liberal Democrats: The Liberal Democrats were the junior member of the 2010–15 coalition government, having won 57 seats. They contested 631 seats, and like Labour, only not contesting the Speaker's seat and all seats in Northern Ireland.
• UK Independence Party (or UKIP): UKIP won the fourth-most votes at the 2010 election, but failed to win any seats. They went into the election with two seats; due to winning two by-elections. They also won the most votes of any British party at the 2014 European election. It contested 624 seats across the United Kingdom.^{[n 3]}
• Green Party: The Green Party went into the election with only one seat. However, they won the fourth-most votes in the 2014 European election. In 2010, Caroline Lucas became the party's first ever MP. In this election they received 3.8% of the vote. This made them the sixth largest party in terms of how many people voted for them. They stood in 573 seats.

Northern Ireland

The main parties in Northern Ireland in order of their number of seats were:

• Democratic Unionist Party (DUP): the DUP won eight seats in 2010, making it the largest party in Northern Ireland and the fourth biggest in the UK. The party also won the 2011 Northern Ireland Assembly election, and came in second out of the Northern Irish parties at the 2014 European election. It contested 16 of the 18 Northern Irish constituencies, having entered into an electoral pact to abstain from the two other seats with the Ulster Unionist Party.
• Sinn Féin: Sinn Féin won the most votes in Northern Ireland in 2010, but came second in the number of seats, winning five. They came second at the 2011 Northern Ireland Assembly election and they came in first out of the Northern Irish parties in the 2014 European election. In the House of Commons Sinn Féin are abstentionists, and so they have never taken up the seats that they have won there. The party also operates in Ireland, where it does take seats in parliament. It stood in all 18 Northern Irish constituencies.
• Social Democratic and Labour Party (or the SDLP): The SDLP third in terms of both votes and seats in the 2010 general election and 2011 Northern Ireland Assembly election, and fourth in the 2014 European election. Going into this election, the party had three MPs. The SDLP has a relationship with the Labour Party, with the SDLP's MPs generally following the Labour whip. In the case of a hung parliament, the party would have entered into a confidence-and-supply-agreement with the party.^[32] They contested all 18 Northern Irish constituencies at the election.
• Ulster Unionist Party (or the UUP): in 2010 the UUP entered into an electoral alliance with the Conservative Party, and finished fourth in terms of votes in Northern Ireland, but won no seats. The party has one MEP, having placed third in the 2014 European elections. They came fourth in the 2011 Northern Ireland Assembly election. The UUP contested 15 of the 18 Northern Irish seats; the party did not run in two seats because of its electoral pact with the DUP, and also did not nominate a candidate against former party member, Sylvia Hermon.^[33]
• Alliance Party of Northern Ireland: The Alliance Party had one MP going into this election, Naomi Long, who had been elected for the first time in 2010. They came fifth in the 2010 election by vote share. They have a relationship with the Liberal Democrats. However, the Alliance's one MP elected in 2010 sat on the opposition benches in the Commons and not with the Liberal Democrats on the government benches. The party contested all 18 Northern Irish constituencies in 2015.

Smaller parties in Northern Ireland included the Traditional Unionist Voice, who won no seats at this election but had one member of the Northern Ireland Assembly, the Conservatives and UKIP (both are major parties in the rest of the UK, but are minor parties here).^[34]

Scotland

• Scottish National Party (or the SNP): The SNP only contested seats in Scotland and stood in all 59 Scottish constituencies. The party received the second-most votes in Scotland and the sixth-most overall in 2010, winning six seats. It won the 2011 election to the Scottish Parliament and had a surge of support since the Scottish independence referendum in September 2014, in which it was the main political party behind the losing Yes campaign.^[35] Most projections suggested that it would be the third-largest party overall after the 2015 election, in terms of seats won, overtaking the Liberal Democrats.^[23]

Smaller parties in Scotland include the Scottish Libertarian Party, but none of the smaller parties make much of an impact in general elections in Scotland.

Wales

• Plaid Cymru: led by Leanne Wood, who was a member of the Welsh Assembly and did not stand in the general election. Plaid Cymru organises only in Wales, where it contested all forty Welsh constituencies. The party has three MPs and was fourth in Wales (eighth overall) by vote share in 2010, later finishing third in the 2011 Welsh Assembly elections.

Wales has a number of smaller parties which, again, do not tend to make much impact in the general elections. In 2015, the Labour Party continued to dominate Welsh politics at the general elections.

Pacts and possible coalitions

Coalitions have been rare in the United Kingdom, because the first-past-the-post system has usually led to one party winning an overall majority in the Commons. However, with the outgoing Government being a coalition and with opinion polls not showing a large or consistent lead for any one party, there was much discussion about possible post-election coalitions or other arrangements, such as confidence and supply agreements.^[36]

Some UK political parties that only stand in part of the country have reciprocal relationships with parties standing in other parts of the country. These include:

• Labour (in Great Britain) and SDLP (in Northern Ireland)
• Liberal Democrats (in Great Britain) and Alliance (in Northern Ireland)
• SNP (in Scotland) and Plaid Cymru (in Wales)
  • Plaid Cymru also recommended supporters in England to vote Green,^[37] while the SNP leader Nicola Sturgeon said she would vote for Plaid Cymru were she in Wales, and Green were she in England.^[38] However, Sturgeon also said that, if their candidate was the most progressive, she would vote for Labour were she in England.^[39]
• Green Party of England and Wales (in England and Wales), Scottish Greens (in Scotland) and the Green Party in Northern Ireland (in Northern Ireland)

On 17 March 2015 the Democratic Unionist Party and the Ulster Unionist Party agreed an election pact, whereby the DUP would not stand candidates in Fermanagh and South Tyrone (where Michelle Gildernew, the Sinn Féin candidate, won by only four votes in 2010) and in Newry and Armagh. In return the UUP would stand aside in Belfast East and Belfast North. The SDLP rejected a similar pact suggested by Sinn Féin to try to ensure that an agreed nationalist would win that constituency.^[40][41][42] The DUP also called on voters in Scotland to support whichever pro-Union candidate was best placed to beat the SNP.^[43]

Candidates

The deadline for parties and individuals to file candidate nomination papers to the acting returning officer (and the deadline for candidates to withdraw) was 4 p.m. on 9 April 2015.^{[44][45][46][47]} The total number of candidates was 3,971; the second-highest number in history, slightly down from the record 4,150 candidates at the last election in 2010.^[31][48]

There were a record number of female candidates standing in terms of both absolute numbers and percentage of candidates: 1,020 (26.1%) in 2015, up from 854 (21.1%) in 2010.^[31][48] The proportion of female candidates for major parties ranged from 41% of Alliance Party candidates to 12% of UKIP candidates.^[49] According to UCL's Parliamentary Candidates UK project^[50] the major parties had the following percentages of black and ethnic minority candidates: the Conservatives 11%, the Liberal Democrats 10%, Labour 9%, UKIP 6%, the Greens 4%.^[51] The average age of the candidates for the seven major parties was 45.^[50]

The youngest candidates were all aged 18: Solomon Curtis (Labour, Wealden); Niamh McCarthy (Independent, Liverpool Wavertree); Michael Burrows (UKIP, Inverclyde); Declan Lloyd (Labour, South East Cornwall); and Laura-Jane Rossington (Communist Party, Plymouth Sutton and Devonport).^[52][53][54] The oldest candidate was Doris Osen, 84, of the Elderly Persons' Independent Party (EPIC), who was standing in Ilford North.^[53] Other candidates aged over 80 included three long-serving Labour MPs standing for re-election: Sir Gerald Kaufman (aged 84; Manchester Gorton), Dennis Skinner (aged 83; Bolsover) and David Winnick (aged 81; Walsall North).

A number of candidates—including two for Labour^[55][56] and two for UKIP^[57][58] – were suspended from their respective parties after nominations were closed. Independent candidate Ronnie Carroll died after nominations were closed.^[59]

By party

Issues

National daily newspapers

National Sunday newspapers

Predictions one month before the vote

The first-past-the-post system used in UK general elections means that the number of seats won is not closely related to vote share.^[155] Thus, several approaches were used to convert polling data and other information into seat predictions. The table below lists some of the predictions. ElectionForecast was used by Newsnight and FiveThirtyEight. May2015.com is a project run by the New Statesman magazine.^[156]

Seat predictions draw from nationwide polling, polling in the constituent nations of Britain and may additionally incorporate constituency level polling, particularly the Ashcroft polls. Approaches may or may not use uniform national swing (UNS). Approaches may just use current polling, i.e. a "nowcast" (e.g. Electoral Calculus, May2015.com and The Guardian), or add in a predictive element about how polling shifts based on historical data (e.g. ElectionForecast and Elections Etc.).^[157] An alternative approach is to use the wisdom of the crowd and base a prediction on betting activity: the Spreadex and Sporting Index columns below cover bets on the number of seats each party will win with the midpoint between asking and selling price, while FirstPastThePost.net aggregates the betting predictions in each individual constituency. Some predictions cover Northern Ireland, with its distinct political culture, while others do not. Parties are sorted by current number of seats in the House of Commons:

Other predictions were published.^[165] An election forecasting conference on 27 March 2015 yielded 11 forecasts of the result in Great Britain (including some included in the table above).^[166] Averaging the conference predictions gives Labour 283 seats, Conservatives 279, Liberal Democrats 23, UKIP 3, SNP 41, Plaid Cymru 3 and Greens 1.^[167] In that situation, no two parties (excluding a Lab-Con coalition) would have been able to form a majority without the support of a third. On 27 April, Rory Scott of the bookmaker Paddy Power predicted Conservatives 284, Labour 272, SNP 50, UKIP 3, and Greens 1.^[168] LucidTalk for the Belfast Telegraph predicted for Northern Ireland: DUP 9, Sinn Féin 5, SDLP 3, Sylvia Hermon 1, with the only seat change being the DUP gaining Belfast East from Alliance.^[169][170]

Final predictions before the vote

Percentage shares of votes, as predicted in the first week of May:

Exit poll

An exit poll, collected by Ipsos MORI and GfK on behalf of the BBC, ITN and Sky News, was published at 10 pm at the end of voting. It interviewed around 22,000 people across a sample of 133 constituencies:^[185]

More information Parties, Seats ...

Parties		Seats	Change
	Conservative Party	316	10
	Labour Party	239	19
	Scottish National Party	58	52
	Liberal Democrats	10	47
	UK Independence Party	2	2
	Green Party	2	1
	Others	23	N/A
Conservatives 10 short of majority

Close

This predicted the Conservatives to be 10 seats short of an absolute majority, although with the 5 predicted Sinn Féin MPs not taking their seats, it was likely to be enough to govern. (In the event, Michelle Gildernew lost her seat, reducing the number of Sinn Féin MPs to 4.)^[186]

The exit poll was markedly different from the pre-election opinion polls,^[187] which had been fairly consistent; this led many pundits and MPs to speculate that the exit poll was inaccurate, and that the final result would have the two main parties closer to each other. Former Liberal Democrat leader Paddy Ashdown vowed to "eat his hat" and former Labour "spin doctor" Alastair Campbell promised to "eat his kilt" if the exit poll, which predicted huge losses for their respective parties, was right.^[188]

As it turned out, the results were even more favourable to the Conservatives than the poll predicted, with the Conservatives obtaining 330 seats, an absolute majority.^[189] Ashdown and Campbell were presented with hat- and kilt-shaped cakes (labelled "eat me") on BBC Question Time on 8 May.^[188]

Opinion polling inaccuracies and scrutiny

With the eventual outcome in terms of both votes and seats varying substantially from the bulk of opinion polls released in the final months before the election, the polling industry received criticism for their inability to predict what was a surprisingly clear Conservative victory. Several theories have been put forward to explain the inaccuracy of the pollsters. One theory was that there had simply been a very late swing to the Conservatives, with the polling company Survation claiming that 13% of voters made up their minds in the final days and 17% on the day of the election.^[190] The company also claimed that a poll they carried out a day before the election gave the Conservatives 37% and Labour 31%, though they said they did not release the poll (commissioned by the Daily Mirror) on the concern that it was too much of an outlier with other poll results.^[191]

However, it was reported that pollsters had in fact picked up a late swing to Labour immediately prior to polling day, not the Conservatives.^[192] It was reported after the election that private pollsters working for the two largest parties actually gathered more accurate results, with Labour's pollster James Morris claiming that the issue was largely to do with surveying technique.^[193] Morris claimed that telephone polls that immediately asked for voting intentions tended to get a high "Don't know" or anti-government reaction, whereas longer telephone conversations conducted by private polls that collected other information such as views on the leaders' performances placed voters in a much better mode to give their true voting intentions.^{[citation needed]} Another theory was the issue of 'shy Tories' not wanting to openly declare their intention to vote Conservative to pollsters.^[194] A final theory, put forward after the election, was the 'Lazy Labour' factor, which claimed that Labour voters tend to not vote on polling day whereas Conservative voters have a much higher turnout.^[195]

The British Polling Council announced an inquiry into the substantial variance between the opinion polls and the actual election result.^[196][197] The inquiry published preliminary findings in January 2016, concluding that "the ways in which polling samples are constructed was the primary cause of the polling miss".^[198] Their final report was published in March 2016.^[199]

The British Election Study team have suggested that weighting error appears to be the cause.^[200]

Geographic voting distribution

One result of the 2015 general election was that a different political party won the popular vote in each of the countries of the United Kingdom.^[207] This was reflected in terms of MPs elected: The Conservatives won in England with 319 MPs out of 533 constituencies,^[208] the SNP won in Scotland with 56 out of 59,^[209] Labour won in Wales with 25 out of 40,^[210] and the Democratic Unionist Party won in Northern Ireland with 8 out of 18.^[211]

Outcome

Despite most opinion polls predicting that the Conservatives and Labour were neck and neck, the Conservatives secured a surprise victory after having won a clear lead over their rivals and incumbent Prime Minister David Cameron was able to form a majority single-party government with a working majority of 12 (in practice increased to 15 due to Sinn Féin's four MPs' abstention). Thus the result bore resemblance to 1992.^[212] The Conservatives gained 38 seats while losing 10, all to Labour; Employment Minister Esther McVey, in Wirral West, was the most senior Conservative to lose her seat. Cameron became the first Prime Minister since Lord Salisbury in 1900 to increase his popular vote share after a full term, and is sometimes credited as being the only Prime Minister other than Margaret Thatcher (in 1983) to be re-elected with a greater number of seats for his party after a 'full term'^{[n 4]}.^[213]

The Labour Party polled below expectations, winning 30.4% of the vote and 232 seats, 24 fewer than its previous result in 2010—even though in 222 constituencies there was a Conservative-to-Labour swing, as against 151 constituencies where there was a Labour-to-Conservative swing.^[214] Its net loss of seats were mainly a result of its resounding defeat in Scotland, where the Scottish National Party took 40 of Labour's 41 seats, unseating key politicians such as shadow Foreign Secretary Douglas Alexander and Scottish Labour leader Jim Murphy. Labour gained some seats in London and other major cities, but lost a further nine seats to the Conservatives, recording its lowest share of the seats since the 1987 general election.^[215] Ed Miliband subsequently tendered his resignation as Labour leader.

The Scottish National Party had a stunning election, rising from just 6 seats to 56 – winning all but 3 of the constituencies in Scotland and securing 50% of the popular vote in Scotland.^[209] They recorded a number of record breaking swings of over 30% including the new record of 39.3% in Glasgow North East. They also won the seat of former Prime Minister Gordon Brown, overturning a majority of 23,009 to win by a majority of 9,974 votes and saw Mhairi Black, then a 20-year-old student, defeat Labour's Shadow Foreign Secretary Douglas Alexander with a swing of 26.9%.

The Liberal Democrats, who had been in government as coalition partners, suffered the worst defeat they or the previous Liberal Party had suffered since the 1970 general election.^[216] Winning just eight seats, the Liberal Democrats lost their position as the UK's third party and found themselves tied in fourth place with the Democratic Unionist Party of Northern Ireland in the House of Commons, with Nick Clegg being one of the few MPs from his party to retain his seat. The Liberal Democrats gained no seats, while losing 49 in the process—of them, 27 to the Conservatives, 12 to Labour, and 10 to the SNP. The party also lost their deposit in 341 seats, the same number as in every general election from 1979 to 2010 combined.

The UK Independence Party (UKIP) was only able to hold one of its two seats, Clacton, gaining no new ones despite increasing its vote share to 12.9% (the third-highest share overall). Party leader Nigel Farage, having failed to win the constituency of South Thanet, tendered his resignation, although this was rejected by his party's executive council and he stayed on as leader.

In Northern Ireland, the Ulster Unionist Party returned to the Commons with two MPs after a five-year absence, gaining one seat from the Democratic Unionist Party and one from Sinn Féin, while the Alliance Party lost its only Commons seat to the DUP, despite an increase in total vote share.^[217]

Voter demographics

Gender

The election led to an increase in the number of female MPs, to 191 (29% of the total, including 99 Labour; 68 Conservative; 20 SNP; 4 other) from 147 (23% of the total, including 87 Labour; 47 Conservative; 7 Liberal Democrat; 1 SNP; 5 other). As before the election, the region with the largest proportion of women MPs was North East England.^[221]

Seats which changed allegiance

111 seats changed hands compared to the result in 2010 plus three by-election gains reverted to the party that won the seat at the last general election in 2010 (Bradford West, Corby and Rochester and Strood).

General election records broken in 2015

Resignations

On 8 May, three party leaders announced their resignations within an hour of each other:^[226] Ed Miliband (Labour) and Nick Clegg (Liberal Democrat) resigned due to their parties' worse-than-expected results in the election, although both had been re-elected to their seats in Parliament.^{[227][228][229][230]} Nigel Farage (UKIP) offered his resignation because he had failed to be elected as MP for Thanet South, but said he might re-stand in the resulting leadership election. However, on 11 May, the UKIP executive rejected his resignation on the grounds that the election campaign had been "a great success",^[231] and Farage agreed to continue as party leader.^[232]

Alan Sugar, a Labour peer in the House of Lords, also announced his resignation from the Labour Party for running what he perceived to be an anti-business campaign.^[233]

In response to Labour's poor performance in Scotland, Scottish Labour leader Jim Murphy initially resisted calls for his resignation by other senior party members. Despite surviving a no-confidence vote by 17–14 from the party's national executive, Murphy announced he would step down as leader on or before 16 May.^[234]

Financial markets

Financial markets reacted positively to the result, with the pound sterling rising against the Euro and US dollar when the exit poll was published, and the FTSE 100 stock market index rising 2.3% on 8 May. The BBC reported: "Bank shares saw some of the biggest gains, on hopes that the sector will not see any further rises in levies. Shares in Lloyds Banking Group rose 5.75% while Barclays was 3.7% higher", adding: "Energy firms also saw their share prices rise, as Labour had wanted a price freeze and more powers for the energy regulator. British Gas owner Centrica rose 8.1% and SSE shares were up 5.3%." BBC economics editor Robert Peston noted: "To state the obvious, investors love the Tories' general election victory. There are a few reasons. One (no surprise here) is that Labour's threat of breaking up banks and imposing energy price caps has been lifted. Second is that investors have been discounting days and weeks of wrangling after polling day over who would form the government – and so they are semi-euphoric that we already know who's in charge. Third, many investors tend to be economically Conservative and instinctively Conservative."^[235]

Electoral reform

The disparity between the numbers of votes and the number of seats obtained by the smaller parties gave rise to increased calls for replacement of the 'first-past-the-post' voting system with a more proportional system. For example, UKIP had 3.9 million votes per seat, whereas SNP had just 26,000 votes per seat, about 150 times greater representation for each vote cast. UKIP stood in 10 times as many seats as the SNP. Noting that UKIP's 13% share of the overall votes cast had resulted in the election of just one MP, Nigel Farage argued that the UK's voting system needed reforming, saying: "Personally, I think the first-past-the-post system is bankrupt."^[236]

Re-elected Green Party MP Caroline Lucas agreed, saying: "The political system in this country is broken [...] It's ever clearer tonight that the time for electoral reform is long overdue, and it's only proportional representation that will deliver a Parliament that is truly legitimate and better reflects the people it is meant to represent."^[237]

Daily Telegraph investigation of abuse of Wikipedia

Following the election, The Daily Telegraph detailed changes to Wikipedia pages made from computers with IP addresses inside Parliament raising suspicion that "MPs or their political parties deliberately hid information from the public online to make candidates appear more electable to voters" and a deliberate attempt to hide embarrassing information from the electorate.^[238]

Telegraph Media Group fined

On 21 December 2015, the UK Information Commissioner's Office fined the Telegraph Media Group £30,000 for sending 'hundreds of thousands of emails on the day of the general election urging readers to vote Conservative ... in a letter from Daily Telegraph editor Chris Evans, attached to the paper's usual morning e-bulletin'. The ICO concluded that subscribers had not expressed their consent to receive this kind of direct marketing.^[239]

Election petition

Four electors from Orkney and Shetland lodged an election petition on 29 May 2015 attempting to unseat Alistair Carmichael and force a by-election^[240][241] over what became known as 'Frenchgate'.^[242] The issue centred around the leaking of a memo from the Scotland Office about comments allegedly made by the French ambassador Sylvie Bermann about Nicola Sturgeon, claiming that Sturgeon had privately stated she would "rather see David Cameron remain as PM", in contrast to her publicly stated opposition to a Conservative government.^[243] The veracity of the memo was quickly denied by the French ambassador, French consul general and Sturgeon.^[244] At the time of the leak, Carmichael denied all knowledge of the leaking of the memo in a television interview with Channel 4 News.^[245] but after the election Carmichael accepted the contents of the memo were incorrect, admitted that he had lied, and that he had authorised the leaking of the inaccurate memo to the media after a Cabinet Office enquiry identified Carmichael's role in the leak. On 9 December, an Election Court decided that although he had told a "blatant lie" in a TV interview, it had not been proven beyond reasonable doubt that he had committed an "illegal practice" under the Representation of the People Act^[246] and he was allowed to retain his seat.^[247]

Party election spending investigations

At national party level, the Electoral Commission fined the three largest parties for breaches of spending regulations, levying the highest fines since its foundation:^[248] £20,000 for Labour in October 2016,^[249] £20,000 for the Liberal Democrats in December 2016,^[250] and £70,000 for the Conservative Party in March 2017.^[251][248]

The higher fine for the Conservatives reflected both the extent of the wrongdoing (which extended to the 2014 parliamentary by-elections in Clacton, Newark and Rochester and Strood) and 'the unreasonable uncooperative conduct by the Party'.^[252][248] The commission also found that the Party Treasurer, Simon Day, may not have fulfilled his obligations under the Political Parties, Elections and Referendums Act 2000 and referred him for investigation to the Metropolitan Police Service.^[253]

At constituency level, related alleged breaches of spending regulations led to 'unprecedented'^[251] police investigations for possible criminal conduct of between 20 and 30 Conservative Party MPs. On 9 May 2017, the Crown Prosecution Service decided not to prosecute the vast majority of suspects, saying that "in order to bring a charge, it must be proved that a suspect knew the return was inaccurate and acted dishonestly in signing the declaration. Although there is evidence to suggest the returns may have been inaccurate, there is insufficient evidence to prove to the criminal standard that any candidate or agent was dishonest."^[254] On 2 June 2017, charges were brought under the Representation of the People Act 1983 against Craig Mackinlay, who was elected Conservative MP for South Thanet in 2015, his agent Nathan Gray, and a party activist, Marion Little.^[255][256] Appearing at Westminster Magistrates' Court on 4 July 2017, the three pleased not guilty and were released on unconditional bail pending an appearance at Southwark Crown Court on 1 August 2017.^[257][258] The investigation of Party Treasurer Simon Day remained ongoing.^[259]

In 2016–18, the European Parliament found that UKIP had unlawfully spent over €173,000 of EU funding on the party's 2015 UK election campaign, via the Alliance for Direct Democracy in Europe and the affiliated Institute for Direct Democracy. The Parliament required the repayment of the mis-spent funds and denied the organisations some other funding.^{[260][261][262]} It also found that UKIP MEPs had unlawfully spent EU money on other assistance for national campaigning purposes during 2014–16 and docked their salaries to recoup the mis-spent funds.^{[263][264][265]}