10 Downing Street

10 Downing Street in London is the official residence and office of the First Lord of the Treasury, an office held concurrently by the prime minister of the United Kingdom. Colloquially known as Number 10, the building is located in Downing Street, off Whitehall in the City of Westminster.

It is over 300 years old, is a Grade I listed building, and contains approximately 100 rooms. A private residence for the prime minister occupies the third floor and there is 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 hosted. At the rear is an interior courtyard and a terrace overlooking a 1⁄2-acre (0.2 ha) garden. Number 10 is adjacent to St James's Park, approximately 3⁄4 mile (1.2 km) from Buckingham Palace, the official residence of the British monarch in London, and is near the Palace of Westminster, the meeting place of both Houses of Parliament.

Originally three houses, Number 10 was offered to Robert Walpole by King George II in 1732. Walpole accepted on the condition that the gift was to the office of First Lord of the Treasury. The post of First Lord of the Treasury has, for much of the 18th and 19th centuries and invariably since 1905, been held by the prime minister. Walpole commissioned William Kent to join the three houses and it is this larger house that is known as Number 10 Downing Street.

Despite its size and convenient location near to Parliament, few early prime ministers lived at 10 Downing Street. Costly to maintain, neglected, and run-down, Number 10 was scheduled to be demolished several times, but the property survived and became linked with many statesmen and events in British history. In 1985 Prime Minister Margaret Thatcher said Number 10 had become "one of the most precious jewels in the national heritage".

The Prime Minister's Office, for which the terms Downing Street and Number 10 are metonyms, lies within the 10 Downing Street building and is part of the Cabinet Office. It is staffed by civil servants and special advisers.

10 Downing Street is property of His Majesty’s Government. Its registered legal title is held in the name of the secretary of state for housing, communities and local government, and the secretary of state is a corporation sole.

Number 10 Downing Street was originally three properties: a mansion overlooking St James's Park called "the House at the Back", a town house behind it, and a cottage. The town house, from which the modern building gets its name, was one of several built by George Downing between 1682 and 1684.

Downing, a noted spy for Oliver Cromwell and later King Charles II, invested in property and acquired considerable wealth. In 1654, he purchased the lease on land south of St James's Park, adjacent to the House at the Back within walking distance of parliament. Downing planned to build a row of terraced town houses "for persons of good quality to inhabit in ..." The street on which he built them now bears his name, and the largest became part of Number 10 Downing Street.