No 9 Downing Street has served as the entrance to the Privy Council Office since 2001 and currently houses both the Leader's office and the Department for Exiting the European Union.
No. 10 Downing Street is the official office and residence of the First Lord of the Treasury, whose office has been held by the Prime Minister without exception since 1735.
No. 11 Downing Street has been the residence of the Second Lord of the Treasury since 1828.
No. 12 Downing Street, formerly the official residence of the Leader of the House, currently houses the Prime Minister's Press Office, as well as the Marketing and Communications Office.
Since the existence of these Houses, Ministers have by mutual consent occupied the Houses which best meet their needs. Thus, number 11 is sometimes occupied not by the Chancellor of the Exchequer but by the Cabinet member who has been designated as Deputy Prime Minister; whether or not he takes that title is immaterial. This handling was particularly common in coalition governments. Sometimes ministers used their provided living quarters only for official occasions and lived elsewhere.
During his tenure, which began in 1881, William Gladstone claimed the flats at numbers 10, 11 and 12 for himself and his family. This was appropriate as he was both Chancellor of the Exchequer and Prime Minister at the time.
Following the 1997 House of Commons election, in which the Labour Party took over the government, a change of residence was made between the two incumbents, as the married Tony Blair still had three children living at home, while his colleague Gordon Brown was unmarried when he took over as Chancellor of the Exchequer. Although Number 10 remained the Prime Minister's official residence and official residence, Blair moved his family into the more spacious Number 11, while Brown lived in the smaller Number 10 apartment.
Houses 10, 11 and 12 are connected to each other on several floors by wall openings, so that they are rather to be considered as a building complex. Also, the plots of the three buildings form a single garden at the back without partitions.
The actual private living quarters of the Prime Minister, insofar as they are used for these purposes, are located in the roof slope of the 4th floor, which was extended during a core renovation in the 1960s. Prior to this, the Prime Ministers still used the garden-facing rooms on the 1st floor for residential purposes. Today, these are used for representation and the reception of guests.
