In the 1870s, one of Gladstone's private secretaries, William Gurdon, produced a form letter for answering various types of frequent enquiry. His rules were recorded in the "Book of Knowledge" which was updated by Gladstone's later private secretaries.
By the beginning of this century, Salisbury and Balfour could still read and reply personally to a good part of the correspondence which came into the office each day. The prime minister then had three private secretaries who effectively maintained links with Parliament, the media, Cabinet and the Palace.
In 1970 Ted Heath's support was still in single figures and No 10 was as much a home as an office. Heath's political secretary, a young Douglas Hurd, commented, "It is hard to imagine anyone governing anything substantial from No 10." Tony Blair today is backed by nearly 40 staff who work on party policy and media relations on his behalf.
Some of Blair's predecessors fought to strengthen their support. Lloyd George in 1916 established a Garden Suburb (a forerunner of today's Policy Unit), and a Cabinet Office, to systematise Cabinet's work, as well as recruiting a number of secretaries to do the typing. The latter were situated in two basement rooms facing the garden and were known as the Garden Room Girls. Lloyd George's neglect of the Cabinet and House of Commons, and his reputation as a wrecker of the Liberal Party, meant that his more powerful office was condemned as a form of presidentialism. When he fell from office in 1922, the Garden Suburb was abolished and the Cabinet Office trimmed back.
In 1964 Harold Wilson brought in a handful of political appointees, including the redoubtable Marcia Williams. They were not made welcome and 30 years later retired civil servants still shudder when they recall working in No 10 in the late 1960s. Having formalised the office of political secretary for Mrs Williams in 1964 Wilson innovated again in 1974, creating the Policy Unit which still stands today.
The first head of Mrs Thatcher's Policy Unit, Sir John Hoskyns, was also given a frosty reception by officials in No 10. The strong opposition she faced from the Foreign Office and the rest of Whitehall when she appointed her own foreign policy adviser in 1982 (Sir Anthony Parsons) helped to dissuade Mrs Thatcher from setting up a Prime Minister's Department, absorbing members of Policy Unit, Cabinet Office and Central Policy Review Staff. The later indiscretions of her economic adviser Sir Alan Walters exacerbated differences between herself and her Chancellor Nigel Lawson and led to the latter's resignation.
Tony Blair is not the first prime minister to be accused of cronyism, or having people around with whom he feels comfortable. Gladstone and Salisbury relied on relations to help them in No 10. Asquith's principal private secretary became his son-in-law and Churchill had his son-in-law, Christopher Soames, as his parliamentary private secretary. Lloyd George was surrounded by his so-called Taffia and his mistress Frances Stevenson.
Over the century the Prime Minister's Office has become larger and more differentiated. The dividing line between party-political and civil-service activity has became clearer where once it was opaque. Until Lloyd George it made little sense to talk of separate political and official institutions within No 10.
Because Whitehall dreads civil servants going native, it likes to move the private secretaries out of No 10 every three years or so. Mrs Thatcher's breach of this convention, by keeping Bernard Ingham and Charles Powell with her to the end, only reinforced it in the eyes of Whitehall.
Dennis Kavanagh is co-author, with Anthony Seldon, of `The Powers Behind the Prime Minister' (HarperCollins, pounds 19.99)