The First Lord of the Treasury is one of the Lords Commissioners of the Treasury. This role is usually held by the Prime Minister.

Since the 17th century, the Lords Commissioners of the Treasury have collectively carried out duties that were previously held by the Lord High Treasurer (head of Her Majesty’s Treasury).

The Lords Commissioners of the Treasury also include:

the Second Lord of the Treasury - the Chancellor of the Exchequer, who has most of the functional financial responsibilities

Junior Lords Commissioners of the Treasury - other members of the government, usually government whips in the House of Commons

10 Downing Street is the official residence of the First Lord of the Treasury, and not of the Prime Minister.