10 Downing Street, William Pitt's mahogany desk (photo)

Downing Street was named after diplomat Sir George Downing (1623-84). In 1732 George II gave Number 10 and an adjoining house overlooking Horse Guards to first Lord of the Treasury Sir Robert Walpole who employed architect William Kent to join and reburbish them - it has been the official residence of the prime minister ever since. Sir John Soane added panelled rooms in the 1820s and it was extensively remodelled by Raymond Erith 1960-3 and by Quinlan Terry in the late 1980s under Margaret Thatcher. William Pitt the Younger was prime minister 1783-1801 and 1804-6. His desk was photographed in the Green Room in1999.