Beginning in the 17th century, the Treasury was frequently entrusted to a commission, rather than to a single individual, and after 1714, it was always in commission. The commissioners were referred to as Lords Commissioners of the Treasury, and given a number based on seniority. Eventually, the First Lord of the Treasury came to be seen as the natural head of any ministry, and, from Robert Walpole on, began to be known, unofficially, as the prime minister.
Before 1827, the First Lord of the Treasury, when a commoner, also held the office of Chancellor of the Exchequer, while if the First Lord was a peer, the Second Lord would usually serve as Chancellor. Since 1827, the Chancellor of the Exchequer has always been Second Lord of the Treasury when he has not also been the Prime Minister. By convention, the other Lords Commissioners of the Treasury are Government Whips in the House of Commons.
Official Residences
Contrary to popular impression, 10 Downing Street is the residence of the First Lord of the Treasury, not the prime minister. There is in fact no prime ministerial residence apart from Chequers, a country house in Buckinghamshire used as a weekend and holiday home; however, all modern prime ministers have simultaneously been First Lord of the Treasury, so 10 Downing Street has come to be closely identified with the premiership.
Similarly, 11 Downing Street is the residence of the Second Lord of the Treasury, not the residence of the Chancellor of the Exchequer; given that all chancellors since 1755 who were not themselves prime minister have also been Second Lord, people often wrongly presume that 11 Downing Street is the Chancellor's residence.
