9 Downing Street is one of the buildings situated on Downing Street in the City of Westminster in London, England.
Under the current government, the building is being used to house the Department for Exiting the European Union and the office of the Chief Whip, and is also the Downing Street entrance to the Privy Council Office.
Formerly the building was part of the more famous 10 Downing Street, official residence of the First Lord of the Treasury, who since the early years of the 19th century has always been the Prime Minister of the United Kingdom. Many internal refurbishments over the years have altered the interior of numbers 10, 11 and 12 to the point that they are all part of a single complex. It was part of a reorganisation in 2001 that the number 9 address was created.
Until 2009, number 9 was home to the Judicial Committee of the Privy Council, which moved to Middlesex Guildhall in August of that year along with the Supreme Court of the United Kingdom.
Although number 9 is currently the address of the office of the Chief Whip, the Chief Whip's official residence is still 12 Downing Street.