Up to the 19th century

The first documented exodus of Britons began during the Anglo-Saxon invasion of Great Britain. A large number of Brythonic-speaking Celts fled or migrated to what is now Brittany on the coast of France, becoming the Bretons.^[21]

The second large-scale British migration came following the Norman Conquest of England, leading to a displacement of English people, mostly dispossessed nobility. They settled in neighboring regions including Ireland and Scandinavia, and as far east as Crimea and Anatolia in the Byzantine Empire.^[22] Englishmen eventually replaced Scandinavians as the main source of recruitment for the Byzantine Emperor’s personal Varangian Guard.^[23]

After the Age of Discovery, the various peoples of the British Isles, and especially the English, were among the earliest and by far the largest communities to emigrate out of Europe. Indeed, the British Empire's expansion during the first half of the 19th century saw an extraordinary dispersion of the British people, with particular concentrations in Australasia and North America.^[24]

The British Empire was "built on waves of migration overseas by British people",^[25] who left Great Britain, later the United Kingdom, and reached across the globe and permanently affected population structures in three continents.^[24] As a result of the British colonisation of the Americas, what became the United States was "easily the greatest single destination of emigrant British", but in what would become the Commonwealth of Australia the British experienced a birth rate higher than anything seen before, which together with continuing British immigration resulted in a huge outnumbering of indigenous Australians.^[24]

In colonies such as Southern Rhodesia, British Hong Kong, Singapore, Jamaica, Barbados, Malaysia, and the Cape Colony, permanently resident British communities were established, and while never more than a numerical minority, these Britons exercised a dominant influence upon the culture and politics of those lands.^[25] In Australia, Canada, and New Zealand, people of British origin came to constitute the majority of the population, contributing to these states becoming integral to the Anglosphere.^[25]

The British not only emigrated to parts of the British Empire, but also settled in large numbers in parts of the Americas, particularly in the United States and in sizeable numbers in Mexico, Chile and Argentina.

The United Kingdom census, 1861 estimated the number of overseas British to be around 2.5 million. However, it concluded that most of these were "not conventional settlers" but rather "travellers, merchants, professionals, and military personnel".^[24] By 1890, there were over 1.5 million further British-born people living in Australia, Canada, New Zealand, and South Africa.^[24]

British diaspora today

According to The Foreign and Commonwealth Office, there were 13.1 million British nationals living abroad in 2004–05. These figures are taken from the consular annual returns from overseas posts. There is no requirement for UK citizens to register with British missions overseas, so these figures are therefore based on the most reliable information that can be obtained, e.g. from host government official statistics.^[26]

A 2006 publication from the Institute for Public Policy Research estimated that 5.5 million British-born people lived outside the United Kingdom.^[20]

In terms of outbound expatriation, in 2009, the United Kingdom had the most expatriates among developed OECD countries, with more than three million British living abroad, a figure followed by Germany and Italy.^[27] On an annual basis, emigration from Britain has stood at about 400,000 per year for the past 10 years.^[28]

Living abroad as an expatriate can affect certain rights. In particular:

• ^[29] can only vote in general elections if they have been on a British electoral register at some point in the past 15 years. Otherwise, they are not eligible to vote.^[30][31] This Briefing Paper provides information on the eligibility to vote in UK Parliamentary elections for British citizens living overseas and the government's plans to end the 15-year rule – it's 'votes for life' policy.
• The British Mental Health Act 1983 rules that persons resident abroad do not qualify as "nearest relative" of a person who is ordinarily resident in the United Kingdom, the Channel Islands or the Isle of Man.