Following her appointment as Prime Minister yesterday, Liz Truss has become the third Prime Minister in a row to take office directly as a result of a party leadership election. Ben Worthy explains that taking office in the middle of a parliament has historically not gone well for the incoming Prime Minister, with none of the last three ‘takeover Prime Ministers’ able to complete a full parliamentary term in office.

There are two routes to becoming Prime Minister in the UK. You can either win a general election or triumph in a party leadership election to become head of the largest parliamentary party when a predecessor leaves. As section 2.18 of the Cabinet Manual puts it:

Where a Prime Minister chooses to resign from his or her individual position at a time when his or her administration has an overall majority in the House of Commons, it is for the party or parties in government to identify who can be chosen as the successor.

Prime Minister Liz Truss is a ‘takeover’ leader, securing the post via the second route rather than the first. Remarkably, she will be the fifteenth takeover since 1916 and the second woman appointed mid-term since 2016.

There are some downsides to being a takeover. As the table below shows, takeovers’ time in office tends to be relatively brief. UK prime ministers in the last 100 years have lasted an average of just over five years, equivalent to the maximum length of one parliamentary term. Takeover tenure was considerably shorter at just over 3.6 years, compared with an average of 6.6 years for those who came to office following a general election. The longest takeover premiership was that of John Major, which lasted seven years, and the shortest was Andrew Bonar Law’s seven months (due to ill health).

The most recent takeovers are bywords for difficult, if not failed, premierships. Major (1990–1997), Gordon Brown (2007–2010) and the successive takeovers of Theresa May (2016–2019) and Boris Johnson (2019–2022) stand out as dysfunctional and struggling leaders. All led deeply divided parties and their names are linked to deep crises, whether economic (the Winter of Discontent or Black Wednesday), political (Maastricht or Brexit) or global (COVID-19).