The Aliens Registration Act (Aliens Registration Act 1914) made mandatory the registration of all aliens over the age of 16 with the police and, for the first time in history, the government had some reasonably accurate information concerning migrants in terms of numbers, places of residence, occupations and race. The requirement for aliens to register with the police was renewed by the Aliens Restriction (Amendment) Act 1919. During the First and Second World Wars many migrants who had arrived from countries at war with Britain were interned - that is held in special detention camps - by the British authorities who referred to them as 'enemy aliens'. Many internee records survive in The National Archives and in local archives.
Foreigners living in Britain were regarded as aliens and lacked rights until the had become naturalised. Not all arriavls became naturalised as the process was expensive and unnecessary if they had no property to bequeath, or had no long-term plans to remain in the country.
Children of immigrants born here automatically became British subjects, as did the wives of those who did become naturalised. Britsh women who married aliens became aliens too.
Records normally tell you where the migrant came from. Up to the 19th century it is worth noting the names of other people who bacame subjects at the same time as migrants often moved and acted in groups. From 1509 to 1800 naturalisation details have been published in three volumes by the Huguenot Society of Great Britain and Ireland. From 1801 to 1900, Parliamentary naturalisations 1801-1947 and the Home Secretary's certificates 1844-1871 are all indexed at the FRC and National Archives.
From 1936 naturalisations are closed to public inspection but House of Commons Sessions papers to 1962, arranged annually, give details.
In WW1 and WW2, those enemy aliens who did not return home voluntarily were interned in special camps. The lists of internees are kept by the Red Cross but cannot be searched. There is a very slight coverage at the National Archives and an index to some lists held by the Anglo-German Family History Society.
Immigrant ancestors, who registered with a JP under the Aliens Act 1792, have records at the National Archives.
After WW1 county police forces kept records of immigrants.
Ship passenger lists for immigrants from outside Europe are at the National Archives for 1878-1960. Between 1836 and 1869 there are some ships lists of alien arrivals at the National Archives. If you find a record you are looking for, use Lloyd's register at Guildhall Library to find out where the ship sailed from.
The British Nationality Act of 1949 allows those who were born in British colonies that became independent states before 1949 automatically bacame citizens of that state. Those born in colonies not yet independent became British Subjects without citizenship. If the country then became independent after 1949, people born there could become Citizens of the United Kingdom and Colonies. From 1989, anyone can apply to become a British Citizen provide they can prove at least one grandparent was born in Britain.
Irish Potato Famine - it's cause and why the Irish moved to the UK. This is from Your Family Tree Magazine, May 2005.
Moving Here - a very detailed site covering the history of migration into the UK.
Polish Residents in Scotland - a statistical sourcebook based on the Census of Scotland, 1861-2001. Statistics and history of Polish nationals in Scotland.
Immigrants - Domestic Records Information - Aliens Act, 1836 Certificates of Aliens (HO 2), 1836-1852 & Aliens Act, 1836: Returns and Papers (HO 3), 1836-1869. Details or archives held at the National Archives at Kew.
Jewish Perspectives on UK Records - details of Jewish arrivals into Scotland and the rest of the U.K.