11 Downing Street (commonly known as Number 11), is the official residence of Britain's Second Lord of the Treasury who is formally recognised as the Chancellor of the Exchequer. It is currently the official residence of George Osborne, who was appointed as Chancellor by Prime Minister David Cameron on 11 May 2010.
Number 11 is part of a charcoal-brick Georgian-era converted mansion, overlooking St. James's Park, that consists-from left to right-Number 12, Number 11 and Number 10. Number 11 is located on the left side of Number 10, the official residence of the First Lord of the Treasury, which is recognised as the Prime Minister of the United Kingdom since the earliest era of the 19th century. Number 12, located on the left side of Number 11, is the official residence of the Chief Whip, but it's now used as the Prime Minister's press office.
Many internal refurbishments over years have made it so that three terraced buildings appears as a single complex inside. For instance, one can walk from number 11 to number 10, via an internal connecting door, without using the street doors. When Tony Blair became Prime Minister in 1997 he chose to use Number 11 rather than Number 10 as his actual (as opposed to official) residence, because Number 11 has larger living areas, which he felt were more suitable for his young family.