The definition of Primus Inter Pares, the Latin for First amongst equals is of diminishing use. As early as 1960 the Prime Minister was treated just as any other MP bar a few privileges. Today the PM stands far above other MPs in terms of political influence, media attention and public acknowledgement. The Prime Minister is the head of Government, the First Lord of the Treasury and almost always in modern times, head of the political party which gains the most seats from a General Election.
The title of Minister was first used in the 16th Century to describe officials that the Monarch placed special trust in and was advised by. In the 18th Century the post of First Minister was recognised and the title Prime Minister was first used by Campbell-Bannermanin 1904. The first Minister to hold substantial power was Sir Robert Walpole in 1721, when George I seceded the throne but spent little time residing in Britain (1714).
The diminishing mental health of the Georgian succession lead to a strengthening of the role of the Prime minister until it was accepted that should a Minister hold command of the commons then they should be allowed a mandate for power as long as they never try and encroach the monarch.
The position was not included in any constitution or law but was de facto until the 1937 Ministers of the Crown act.
Today the Prime Minister holds a number of prerogative powers that once belonged to the Crown such as the power to declare war, mobilise troops, the ability to appoint senior civil servants or to bestow honours.
Number 10 Downing Street is considered to be the home of the Prime Minister and his family Tony Blair, in order to house his large family moved next door to number 11, the traditional home of the Chancellor of the Exchequer. The Chief Whip lives at number 12, the only remaining inhabited house on the street. The Prime Minister has a residence at Chequers in Buckinghamshire.