London
London is the seat of the Government of the United Kingdom. Many government departments are based close to the Palace of Westminster, particularly along Whitehall, including the Prime Minister's residence at 10 Downing Street. The British Parliament is often referred to as the "Mother of Parliaments" (although this sobriquet was first applied to England itself by John Bright) because it has been the model for most other parliamentary systems. There are 73 Members of Parliament (MPs) from London, who correspond to local parliamentary constituencies in the national Parliament. As of May 2015, 45 are from the Labour Party, 27 are Conservatives, and one is a Liberal Democrat.

Q: What is the Prime Minister of the UK's official residence?
10 Downing Street