When the British Nationality Act 1948 came into effect on 1 January1949, citizens of the United Kingdom and Colonies who subsequently became naturalised citizens of other countries no longer automatically lost their British nationality. 

Since that date, citizens of a foreign state retained their status as British subjects, citizens of the United Kingdom and Colonies, unless they made a formal declaration of renunciation in front of a British Consul or other British official authorised to accept such declarations.

 A declaration made before a foreign official for the purpose of acquiring another nationality or for any other purpose did not affect the position in United Kingdom law. 

With the enactment of thenew nationality law (British Nationality Act, 1981) which came into effect on 1 January 1983 the provisions for the recognition of dual nationality and the procedure for renunciation of British citizenship have been retained.

T he following relates to US citizenship , information on eligibility for other nationalities please contact the authorities in the relevant country or you nearest Embassy.

Acquisition or use of US citizenship does not jeopardise retention of British citizenship, and there is no objection on the part of British authorities to a dual citizen using a US passport.

A US citizen voluntarily acquiring British citizenship does not lose his US citizenship unless there is an intention to relinquish US citizenship and in most cases it is assumed that Americans who are naturalised in other countries intend to keep their US citizenship.  As a result they have both nationalities. British citizens who are also US citizens are however advised to consult the US Immigration and Naturalisation Service (or if overseas a US Consul) before taking any action which they think might be regarded as inconsistent with their status as US citizens.

The US authorities do require dual citizens to travel out and into United States territory only on US passports.

A British citizen has the right of abode in the United Kingdom and may return and resume residence in Britain at any time, regardless of being a dual national, provided that he has not made a formal declaration of renunciation of British citizenship as described in paragraph one above.  Such persons may in British law exercise any right possessed generally by British citizens, but of course it is their own responsibility to ascertain from the authorities of their second nationality what effect, if any, their action may have on their status as a citizen of that country.

Children born in the United States whose fathers (and for those born after 31 December 1982, either of whose parents) are British citizens may also be British citizens by descent.  The position of such children is explained in a separate memorandum, which may be obtained from the North America Passport Production Centre.

British citizens who are also citizens of another country are advised that theycannot be accorded official British protection when they are in the territory of the other citizenship.  If, under the law of that country,they are liable for any obligation (such as military service) the fact that they are also British citizens does not exempt them from it.