Downing Street

Downing Street is the formal address in London for the senior cabinet ministers, including The Prime Minister who resides in Number 10. The street in Westminster, central London, has been the home of the ministers for over 200 years. The street was built by and named after Sir George Downing (1632–1689). Downing was a diplomat, serving under King Charles II. It was the King that rewarded Downing with the plot of land adjoining St. James's Park upon which Downing Street now stands.

10 Downing Street is the official residence of the British Prime Minister, whilst 11 Downing Street is the home of the Chancellor of the Exchequer.

http://www.number-10.gov.uk/output/Page178.asp