The Prime Minister is the most senior officer of Her Majesty's Government in the United Kingdom (before 1801, the Kingdom of Great Britain). The full title of the office is Prime Minister, First Lord of the Treasury, and Minister for the Civil Service of the United Kingdom of Great Britain and Northern Ireland; although, not all prime ministers have been First Lord of the Treasury. The last prime minister not to have been First Lord was Lord Salisbury (-1902).
Until the 18th century, the monarch's most senior minister could hold any of a number of titles; usually either First Lord, Lord Chancellor, Lord Privy Seal, or one of the Secretaries of State. During the late 18th Century, the term "prime minister" came to be used, as an unofficial title for this most senior minister -- as he was "premier among ministers". In 1905, the title was officially recognized by King Edward VII, when the office was given status within the 'order of precedence' (behind the Archbishop of York). The first "actual" prime minister was Henry Campbell-Bannerman.
The Prime Minister's main responsibilities include setting the direction of the government, appointing members of the Cabinet, coordinating the activities of the Cabinet and government departments, participating in ceremonial occasions, and being the 'face' of the government in the UK and abroad.
The Prime Minister is technically appointed by the Monarch. By convention, he or she always chooses the leader of the party that holds a majority in the House of Commons. If one party does not have a simple majority but two or more parties form a coalition (a rare occurrence, due to the British electoral system), the leader of the coalition is chosen. If the two major parties (Labour, Conservatives) are evenly matched in the House of Commons and neither can form a coalition with minor parties, then the monarch is free to choose the leader of either party as Prime Minister, though in reality that choice would be decided by which one if any was the outgoing prime minister. A choice could not be made until the outgoing prime minister resigned, at which point whichever was the Leader of the Opposition would be asked to form a government.
The Prime Minister and the government must resign upon the passage of a vote of no confidence or the loss of a vote of confidence, unless the defeated Prime Minister seeks a dissolution of parliament which in theory the monarch may refuse but in practice never does. In practice party discipline is usually strong enough to make these votes rare, with only three successful votes of no confidence since 1885. The Prime Minister must also retain the support of his or her party's parliamentary delegation, and in a number of cases including that of Neville Chamberlain and Margaret Thatcher, a party will oust a Prime Minister who appears to be unpopular.
The leader of the second largest party in the House of Commons is termed the 'Leader of Her Majesty's Loyal Opposition'.
In theory, the Prime Minister of the United Kingdom is a primus inter pares (first among equals) in the British Cabinet. In appointing a cabinet the Prime Minister generally includes members of parliament who have political bases of their own and who could potentially be a rival of the Prime Minister. In addition, the Prime Minister retains very limited power to appoint members of the British Civil Service and there is usually tension between elected officials and the civil service. However, in practice, a strong Prime Minister can so dominate government that they become a 'semi-president', that is they fulfil the leadership role in a country in the same way as a president, but not carry out the ceremonial duties of a Head of State. Examples include William Ewart Gladstone, David Lloyd George, Winston Churchill, Margaret Thatcher and Tony Blair.
The office of Prime Minister originated out of the office of First Lord of the Treasury. The First Lord of the Treasury was the senior commissioner responsible for administration of the royal treasury when there was no Lord Treasurer, an office which originated in mediaeval times, and ceased to be used after 1714. It was not, however, until Sir Robert Walpole (1721-1742) that the First Lord of the Treasury became the most powerful minister, and became head of government. Prior to that there was no clear head of government, and the most powerful minister could hold any one of a number of titles (including First Lord of the Treasury and Lord Privy Seal). Even after Walpole, the First Lord was not always the most powerful member of the government, even as recently as 1902 when Lord Salisbury, the Lord Privy Seal, served as Prime Minister while Balfour was First Lord of the Treasury. The Prime Minister remains First Lord of the Treasury, and as such, not as Prime Minister, becomes the tenant of 10 Downing Street.
Although Sir Robert Walpole is considered to be the first Prime Minister, the term Prime Minister and conventions regarding appointment did not originate until later. The term was initially an insult, equivalent to teacher's pet, implying that the minister was the puppet of the monarch. Until Robert Peel's unsuccessful attempt to govern without a majority in Parliament, the monarch still retained a great deal of discretion over the naming of the Prime Minister. The title was not formally adopted (though it had long been used) until the premiership of Sir Henry Campbell-Bannerman (1905-08) when a 'prime minister' was given a status just behind that of the Archbishop of York.
The Prime Minister as First Lord of the Treasury traditionally lives at No. 10 Downing Street, in London. This house was offered by King George II to Sir Robert Walpole as a personal gift. Walpole would not accept it personally, but agreed to receive it in his official capacity as First Lord of the Treasury. Walpole took up residence in 1735. Most subsequent holders of this office have lived there, though some nineteenth century prime ministers chose to live in their own homes. A small number were not First Lord of the Treasury, and so were not entitled to live in Downing Street. Harold Wilson and John Major both lived in Admiralty House for a time. During part of Wilson's time 10 Downing Street underwent major structural renovation involving total rebuilding, while Major moved out in the aftermath of an Provisional IRA mortar attack on the building, while repairs took place. On his election in 1997, Tony Blair took up residence at No. 11 Downing Street, swapping No. 10 with his Chancellor of the Exchequer, Gordon Brown, as the residential accommodation at No. 10 is smaller and Blair had four children while Brown was at the time unmarried (the two houses, and others, are interconnected).
In the eighteenth century, it was oftentimes unclear who was to be considered the Prime Minister, with holders of the offices of First Lord of the Treasury, Lord Privy Seal, and Secretary of State all at one time or another acting as the principal minister in various government. For instance Lord Carteret Secretary of State for the Northern Department from 1742 to 1744 and William Pitt the Elder as Secretary of State for the Southern Department from 1756 to 1757 and again from 1757 to 1761 had many of the powers of a Prime Ministers, although other men held the principal office of Lord Treasurer. This list follows conventional practice in not listing such figures as Prime Ministers. However, when in 1766 Pitt, created Earl of Chatham, was asked by the King to form a ministry, he chose to take the lesser office of Lord Privy Seal, rather than taking over the Treasury. Nevertheless, he is generally considered to have been Prime Minister, due to his having been asked by the King to form a ministry. Such considerations make the earlier part of the list somewhat less authoritative in its determination of who, exactly, was Prime Minister at such times.
Responsibilities
Becoming Prime Minister
Resignation
First Among Equals or 'semi-president'?
Origins of the Office
10 Downing Street
List of Prime Ministers and First Lords of the Treasury