The post of Lord High Treasurer or Lord Treasurer was an English government position and has been a British government position since the Acts of Union of 1707. A holder of the post would be the third-highest-ranked Great Officer of State, below the Lord High Steward and the Lord High Chancellor.
The Lord High Treasurer functions as the head of Her Majesty's Treasury. Since the 17th century, the office has often been held, not by a single person, but placed in commission, so that a board of individuals jointly exercise the powers of the Lord High Treasurer. Such persons are known as Lords Commissioners of the Treasury. The office has been in commission continuously since the resignation of Charles Talbot, 1st Duke of Shrewsbury in 1714.
Although the United Kingdom of Great Britain and Ireland was created in 1801, it was not until the Consolidated Fund Act 1816 that the separate offices of 'Lord High Treasurer of Great Britain' and Lord High Treasurer of Ireland were united into one office as the 'Lord High Treasurer of the United Kingdom of Great Britain and Ireland' on 5 January 1817. The office continued in commission and the commissioners of the old office of 'Lord High Treasurer of Great Britain' continued as the commissioners of the new combined office.
In modern times, by convention, the Lords Commissioners of the Treasury include the Prime Minister of the United Kingdom, usually serving as the 'First Lord of the Treasury', and the Chancellor of the Exchequer, serving as the 'Second Lord of the Treasury'. Other members of the government, usually whips in the House of Commons, are appointed to serve as the junior Lords Commissioners of the Treasury.
The English Treasury seems to have come into existence around 1126, during the reign of Henry I, as the financial responsibilities were separated from the rest of the job that evolved into Lord Great Chamberlain. The Treasury was originally a section of the Royal Household with custody of the King's money. In 1216, a Treasurer was appointed to take control of the Treasury in Winchester. The Treasurer was also an officer of the Exchequer, and supervised the royal accounts. By Tudor times, the Lord High Treasurer had achieved a place among the Great Officers of State, behind the Lord Chancellor and above the Master of the Horse. Under the Treason Act 1351 it was treason to kill him.
During the sixteenth century, the Lord High Treasurer was often considered the most important official of the government, and became a de facto Prime Minister. Exemplifying the power of the Lord High Treasurer is William Cecil, 1st Baron Burghley, who served in the post from 1572 to 1598. During his tenure, he dominated the administration under Elizabeth I.
Since then a system has evolved which has hardly varied. Today, the First Lord of the Treasury is as a rule the Prime Minister, and the Second Lord of the Treasury is the Chancellor of the Exchequer, who has inherited most of the functional financial responsibilities. Next rank the "Junior Lords of the Treasury" who, though theoretically members of the Treasury Board, in practice serve as Government Whips under the Parliamentary Secretary to the Treasury (Chief Whip).