10 Downing Street, colloquially known in the United Kingdom as "Number 10", is the headquarters of the executive branch of the British Government and the official residence and office of the First Lord of the Treasury, a post which, for much of the 18th and 19th centuries and ever since 1905, is also held by the Prime Minister.

Situated in Downing Street in the City of Westminster, London, Number 10 is over three hundred years old and contains approximately one hundred rooms. There is a private residence on the third floor and a kitchen in the basement. The other floors contain offices and conference, reception, sitting and dining rooms where the Prime Minister works, and where government ministers, national leaders and foreign dignitaries are met and entertained. There is an interior courtyard and, in the back, a terrace overlooking a garden of 0.5 acres (2,000 m²). Adjacent to St. James's Park, Number 10 is near to Buckingham Palace, the official London residence of the British monarch, and the Palace of Westminster, the meeting place of both houses of parliament.

Number 10, #10 or variations thereof may refer to:

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