The office of the Prime Minister did not officially exist until December 1905 and the title was not mentioned in the text of any Act of Parliament until the Ministers of the Crown Act 1937. The term 'Prime Minister' was first used of the Earl of Clarendon in the 1660s, but was particularly applied to Sir Robert Walpole, (generally recognised as the first British Prime Minister), from 1730. From this time the Prime Minister was also the First Lord of the Treasury and still occupies Number 10 Downing Street in this capacity today. The functions and powers of the Prime Minister began to formalise and expand after 1867 with the centralisation of party organisations and the Civil Service, the growth of government business, and the increase in Royal prerogatives which the Prime Minister exercises.
The most significant of the Prime Minister's powers and functions include: patronage, which involves appointing and dismissing ministers, (with the Sovereign's approval), advising the Sovereign on many civil and ecclesiastical appointments, recommending the conferment of certain honours and awards; presiding over Cabinet and the Cabinet Committee system; answering questions in Parliament on general policy; and representing Britain in the international arena where he or she exercises the Royal prerogative of signing treaties and declaring war and peace.
The Prime Minister's Office (Number 10) has grown with the role of the Prime Minister. The staff that supports the Prime Minister is made up of civil servants and political appointees. The Private Office consists of seven private secretaries, (civil servants seconded from departments), who each have an area of responsibility. The role of the Private Office includes, handling the Prime Minister's correspondence, managing his or her diary, and collating advice from other departments. Duty Clerks, who manage communications, and the Garden Rooms, who provide secretarial services, support the Private Office. More recently, the Direct Communications Unit handles all correspondence. The Press Office is responsible for liaising with the media, arranging interviews, and responding to questions from the media. Since 1997, longer-term communications and presentational issues are handled by the Strategic Communications unit and briefing material for the whole of Number 10 is provided by the Research and Information Office. Appointments and Honours advise the Prime Minister on a range of appointments.
Since the 1960s, there has been a larger political element in the Prime Minister's Office. The Political Office (1964) manages relations between Number 10 and the party of government, assisting the Prime Minister in his or her capacities as leader of the party and a constituency MP. The Policy Unit (1974) contains a mixture of civil servants and special advisers who provide advice on strategy and policy issues. In addition to the above, the Prime Minister can call for advice from the Cabinet Secretary and any of his or her Ministers and their departmental staff.