There are three circumstances in which the Prime Minister chooses the Government:-
a) After winning an election following a period in Opposition. The Prime Minister will not know whether people who have been impressive in Opposition will be successful as Ministers. As shadow ministers they will have led on a policy area in Parliament but the Prime Minister may shift them to new roles. Robin Cook was the Shadow Health Secretary in Opposition but, on coming to office in 1997, Tony Blair moved him to the post of Foreign Secretary because they did not agree on public service reform.
b) A Prime Minister may retire and the new Prime Minister will take over without an election. The new Prime Minister will have different views on priorities and on senior colleagues. When Callaghan took over from Wilson in 1976 he removed Barbara Castle, even though she had been one of the key figures in the Government, as they had never seen eye to eye on many issues.
c) Prime Ministers regularly change their Government’s while in office to rejuvenate them and move less successful ministers out and bring new people on, or there may be an unexpected resignation that means a Minister has to be replaced.
Factors the Prime Minister will take into account in forming a Government
Key figures in the Parliamentary Party will need to be included. Some of these will be close allies of the Prime Minister, as George Osborne and Michael Gove are with David Cameron. Others may be major figures with support in the Party such as Theresa May and Iain Duncan-Smith in the present Government and Robin Cook and Donald Dewar, who saw through Scottish devolution, were in the Labour Government of 1997. The Prime Minister may actually want potential rivals for his position to be in the Government as they cannot then criticise policies in public because of Cabinet Collective Responsibility. Tony Blair never sacked Gordon Brown despite the conflicts between them and when Michael Heseltine resigned from Margaret Thatcher’s Government he became a focus for opposition on the backbenches and eventually stood against her for the leadership.
The Prime Minister needs to balance the various factions in the party to make sure that they are represented in the Government. For Labour this has meant including both right and left wings of the party, although under Blair, with Gordon Brown very powerful, this instead meant including Blairites and Brownites with personal loyalty being more important than policy differences. Margaret Thatcher had to include those who were not keen on her right-wing economic policies when she took office and only when she felt much more secure was she able to dispense with them. Cameron has included some more Eurosceptic ministers to satisfy the right of the party in the run up to the EU Referendum.
The Prime Minister also needs to ensure that MPs from different parts of the country are represented and, now that there are more women and black MPs, that there is some gender and ethnic balance in the government so that it appears more representative of the country.
Over time a government reshuffle becomes necessary to remove ministers who do not seem to have been competent or who may have shown some disloyalty to the Prime Minister. Blair removed Robin Cook from the Foreign Office in 2001 because he was unlikely to support his policy on Iraq but still kept him in the Government so that he was not a critic on the backbenches . A reshuffle makes it possible to promote new people who are talented, including those recently elected to Parliament or to reward loyalty. The Chief Whip will play an important role in this as the whips, unlike the Prime Minister, are in Parliament all the time talking to MPs and observing how well they perform in debate. Even though a reshuffle allows the PM to exert power, holders of the office such as, Blair and Cameron, actually dislike the process of sacking Ministers and have kept their reshuffles to a minimum.
Prime Ministers often need to give the government a new look, especially as an election nears. Cameron’s pre-election reshuffle removed Ken Clarke who had been in Conservative Governments for some thirty years and promoted new faces, including more women, who would be appearing on television to promote Government policies in the run-up to the 2010 election.