• Video
  • 5 minutes

How do you become British Prime Minister?

Updated Thursday, 1st June 2017
Ever fancied running the country? Dr Richard Heffernan has some advice on the mechanics of the political system.


Britain, like France, is a unitary state, but is a parliamentary democracy, not a semi-presidential system. British voters thus do not directly elect the government or the head of the government, the Prime Minister, and the head of state, the Monarch, is hereditary and not subject to election or appointment. Voters only elect the part of the legislature, the House of Commons, from which the government emerges. For instance, at the 2015 general election, electors voted only to elect an MP in one of the 650 parliamentary constituency in which they lived.

They thereby collectively produce the key part of Britain’s legislature, the House of Commons, and it is from the Commons that the executive, the government, then indirectly emerges. The Conservative government returned in May 2015 had a parliamentary majority of 17, winning 37 percent of the vote and 51 percent of Commons seats. In May 2015 David Cameron became Prime Minister because:

  1. Cameron was the MP for Witney in Oxfordshire;
  2. He had been the leader of the Conservative party since December 2005; and
  3. The Conservative party had a Commons majority

Cameron stopped being Prime Minister in July 2016, when he resigned having lost the EU referendum. The Conservatives, retaining the right to be the government because of their Commons majority, elected Theresa May as their party leader, which meant she then became Prime Minister. This is because:

  1. May is the MP for Maidenhead in Berkshire;
  2. She became the Conservative party leader in July 2016; and
  3. She inherited the Commons majority held by her predecessor, Cameron

Britain has fixed term parliaments, in which an election is to be held in May every five years, but less than a year into her premiership, rather than try to retain her majority in the present parliament, May asked the Commons to agree to a new election, which it did by the required two-thirds majority. An early election is to be held on June 8th, 2017, some three years ahead of schedule. Whenever an election takes place it is the number of Commons seats that you have- having 50 percent plus 1 at least- which enables a party to form a single party government, not the percentage of votes you win at the election. For instance, by winning 355 individual constituencies at the 2005 general election, Labour’s 35 percent of the overall vote meant they won 55 percent of Commons seats, so had a parliamentary majority of 66. In 2010 the Conservatives, unusually, being the largest party in terms of Commons seats, but lacking enough MPs to form a single party majority, had to form a coalition with the third-placed Liberal Democrats.

The Prime Minister can only be Prime Minister because their party elects them as leader and that party secures a Commons majority at an election (either as a single party government, which is usually the case, or, if lacking a Commons majority in a hung parliament where no party has a majority over all other parties combined, in coalition with another party or parties). Government MPs, even should some disagree with certain aspects of their party government’s policy, supply that government after an election and thereafter support its continuation in office until the composition of the Commons changes at the next election- even under a different Prime Minister. A new Prime Minister can thus take office within a parliament—in between elections—when an incumbent stands down. This happened in 1990, when John Major replaced Margaret Thatcher; in 2007, when Gordon Brown replaced Tony Blair, in 2016 when May replaced Cameron; and in 2019 when Boris Johnson replaced Theresa May.   

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CORRECTION: We had originally misplaced Maidenhead in Surrey; we've moved the town back up the A330 to its actual home in Berkshire. 


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