English: The letterbox on the front door of the Prime Minister's official residence at Number10 Downing Street, London. It bears the title the Prime Minister was previously known as, First Lord of the Treasury.

10 Downing Street, the locale of British prime ministers since 1735, vies with the White House as being the most important political building anywhere in the world in the modern era. Behind its black door have been taken the most important decisions affecting Britain for the last 275 years.

In the 20th century alone, the First and Second World Wars were directed from within it, as were the key decisions about the end of the empire, the building of the British nuclear bomb, the handling of economic crises from the Great Depression in 1929 to the great recession of today, and the building up of the welfare state.

Some of the most famous political figures of modern history have lived and worked in Number 10, including Robert Walpole, Pitt the Younger, Benjamin Disraeli, William Gladstone, David Lloyd George, Winston Churchill and Margaret Thatcher.

Number 10 has 3 overlapping functions. It is the official residence of the British Prime Minister: it is their office, and it is also the place where the Prime Minister entertains guests from Her Majesty The Queen to presidents of the United States and other world leaders. The Prime Minister hosts countless receptions and events for a whole range of British and overseas guests, with charitable receptions high up the list.

• Organization: ARMY
• Object Name: No10-2013-005-029
• Category: MOD
• Supplemental Categories: Equipment, Locations
• Keywords: No10, 10 Downing Street, Front door, Letterbox, First Lord of the Treasury, Prime Minister
• Country: UK