In Government (1988–1997)

In the 1987 general election, Arbuthnot was selected to contest the safe Conservative seat of Wanstead and Woodford, as the sitting MP, Patrick Jenkin, was standing down. Arbuthnot won the seat and increased the Conservative majority by over 2,000 to 16,412.^[7]

In 1988 he became the Parliamentary Private Secretary (PPS) to Archie Hamilton at the Ministry of Defence, and in 1990 became the PPS to the Secretary of State for Trade and Industry, Peter Lilley. He entered the John Major government after the 1992 general election when he was made an Assistant Government Whip. He was promoted in 1994 as the Parliamentary Under-Secretary of State at the Department of Social Security. The following year he was promoted to Minister for Defence Procurement, where he remained until the end of the Major government in 1997.

Arbuthnot stated that one of his most pleasing parliamentary achievements was "organising an all-party meeting with the Prime Minister for the exoneration of the pilots of the Chinook that crashed on the Mull of Kintyre in 1994".

In Opposition (1997–2010)

Arbuthnot's seat of Wanstead and Woodford was abolished at the 1997 general election, when he was selected for the new seat of North East Hampshire. In Opposition, he was a member of William Hague's Shadow Cabinet as the Conservative Party's Chief Whip until the 2001 general election when he returned to the backbenches. He was sworn of the Privy Council in 1998.

Arbuthnot returned to the Shadow Cabinet under Michael Howard as Shadow Trade Secretary in 2003, but stood down after the 2005 general election. Since that election he served as the chairman of the influential Defence Select Committee and was Chair of the Special Select Committee set up to scrutinise the Bill that became the Armed Forces Act 2011.^[8] He is a Senior Associate Fellow of the Royal United Services Institute.

Arbuthnot was the parliamentary chairman of the Conservative Friends of Israel.^[9] He was also a member of the Top Level Group of UK Parliamentarians for Multilateral Nuclear Disarmament and Non-proliferation, established in October 2009.^[10]

In the 2009 expenses scandal, Arbuthnot apologised and repaid the public money he had claimed for his swimming pool to be cleaned.^[11] Later that year, he was further criticised in the press for £15,000 of expenses he claimed for upkeep at his second home, including tree surgery and painting his summer house.^[12]

In Government (2010–2015)

In June 2011, Arbuthnot announced that he would not contest the next general election.^[13] On 16 January 2015, he publicly declared his atheism, stating "the pressure on a Conservative politician, particularly of keeping quiet about not being religious, is very similar to the pressure that there has been about keeping quiet about being gay"; he later clarified that he is not gay.^[14]

Arbuthnot has played a pivotal role in helping the subpostmasters affected by the British Post Office scandal to seek justice after the Post Office wrongly – and, it has been alleged, knowingly – sought and obtained convictions for theft, fraud and false accounting against a large number of them.^[15] In September 2023, he supported the £600,000 "take it or leave it" Government compensation for those wrongly convicted saying on The World Tonight on BBC Radio 4, it was "a choice", and that "for some it will be a good way of putting this behind them and getting on with their lives".^[16] Arbuthnot was portrayed by Alex Jennings in Mr Bates vs The Post Office, an ITV dramatisation of the scandal.^[17]