10 Downing Street, colloquially known in the United Kingdom as "Number 10", is the headquarters of Her Majesty's Government and the official residence and office of the First Lord of the Treasury, who is now always the Prime Minister

Prime Minister of the United Kingdom

The Prime Minister of the United Kingdom of Great Britain and Northern Ireland is the Head of Her Majesty's Government in the United Kingdom. The Prime Minister and Cabinet are collectively accountable for their policies and actions to the Sovereign, to Parliament, to their political party and...

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Situated on Downing Street

Downing Street

Downing Street in London, England has for over two hundred years housed the official residences of two of the most senior British cabinet ministers: the First Lord of the Treasury, an office now synonymous with that of Prime Minister of the United Kingdom, and the Second Lord of the Treasury, an...

 in the City of Westminster

City of Westminster

The City of Westminster is a London borough occupying much of the central area of London, England, including most of the West End. It is located to the west of and adjoining the ancient City of London, directly to the east of the Royal Borough of Kensington and Chelsea, and its southern boundary...

, London, Number 10 is one of the most famous addresses in the United Kingdom and the world. Almost three hundred years old, the building contains about one hundred rooms. There is a private residence on the third floor and a kitchen in the basement.