street in Westminster, London, location of some of the principal government offices of the United Kingdom, including the official residence of the prime minister (No. 10): often used figuratively of the British government
after Sir George Downing (1623-84), who owned property there
See Downing Street in American Heritage Dictionary 4
A thoroughfare of Westminster in London, England, off Whitehall. No. 10 Downing Street is the official residence of the first lord of the Treasury, who is usually but not necessarily the prime minister of Great Britain. Nearly all prime ministers have lived at No. 10 since the time of Robert Walpole in the early 1700s.