Boris Johnson has been confirmed as the Conservative Party’s new leader – and the UK’s next prime minister.

Johnson is the eighth post-war prime minister to take office midway through a parliament. The other eight premierships in that period began with victory in a general election.

There is nothing unusual in the mode of Johnson’s accession. The United Kingdom is a parliamentary system and governments derive their authority from being able to command the confidence of the House of Commons. There is no constitutional requirement for a new prime minister to have won an election.

Under the Fixed-term Parliaments Act 2011, the next election is not due until May 2022. Everyone at Westminster knows this. But constitutional reality will not prevent demands for an early general election and for Johnson to win the backing of the country.

The arguments are well-rehearsed. Voters at the last election were choosing a different prime minister and expecting them to serve a full term. The new man wants to do things that were not set out in the party’s manifesto. There should be an election without delay.

Oddly enough, the new Conservative leader made exactly this argument in 2007, when Gordon Brown succeeded Tony Blair. Johnson was seemingly indignant about Brown’s apparent belief that he could “just trample on the democratic will of the British people”.

He is likely to be reminded of this repeatedly. But could he yet avoid similar criticisms by – like Theresa May in April 2017 – surprisingly calling a snap election?

Of the seven post-war prime ministers before Johnson who took office midway through a parliament, almost all toyed with going straight to the country. But only one, Anthony Eden, went ahead and did so. He succeeded Winston Churchill in early April 1955 and won a comfortable parliamentary majority the following month.

Among the remaining six, only Theresa May sought an election very much sooner than was strictly necessary. Her decision to do so, nine months after succeeding David Cameron, caught everyone by surprise. Unfortunately for May, the Conservatives increased their share of the vote but squandered their majority.

The outcome of the June 2017 election is likely to weigh heavy on Johnson’s mind. But so too will the fate of other prime ministers who, having taken office, deferred their chance of going to the country.

Damned if you don’t?

Alec Douglas-Home, prime minister for just short of a year, lost the 1964 general election. James Callaghan, who could have called an election in the autumn of 1978 when Labour was ahead in the polls, ducked the chance. A no-confidence vote in the House of Commons triggered the 1979 election, which was won by the Conservatives and Margaret Thatcher.

Brown similarly ducked an early election in the autumn of 2007. Having encouraged speculation, his decision not to go ahead contributed to a collapse in his authority. He went on to lose in 2010.

Gordon Brown. Credit: Andy Mettler/World Economic Forum/Wikimedia Commons [CC BY-SA 2.0]

John Major fared better. He hoped that the passage of time would enable the Tories to recover from the Poll Tax debacle and Thatcher’s personal unpopularity. His strategy paid off with a victory in 1992, albeit with a much-reduced majority.

A summer vote?

Recent newspaper reports suggest Johnson is gearing up for an election in the summer of 2020. The arguments for waiting at least a year are clear.

From his point of view, waiting will give him a chance to get a feel for the job. It will also give him a chance to experience the trappings of power. Becoming prime minister has been a lifelong ambition and Johnson will want to enjoy his prize.

From his party’s point of view, the polls currently don’t look good. Waiting would give the Tories time to see off the threat posed by the Brexit Party. Johnson has promised that the UK will leave the European Union at the end of October, with or without a deal. Once Britain is out, the Brexit Party will be redundant. Pro-Brexit voters and their donations might return in droves.

The time of year is a further argument against an immediate election. Party activists have planned their summer holidays. Many voters will be away. The disruption could be immense.

There is also the practical matter of securing an early election. Before the Fixed-term Parliaments Act, prime ministers could simply ask the Queen to dissolve parliament. Now they must secure the backing of at least two-thirds of all MPs or else engineer a successful vote of no confidence, ensuring there is no viable alternative government. Johnson will become prime minister on the day before parliament rises for its summer recess. There would be little time to act.

But there are also arguments for not waiting. Seeking an immediate election would enable Johnson to define himself as a leader with gumption, someone who is willing to take chances to break the present deadlock over Brexit. It would enable him to fend off talk of missing mandates and to avoid the charge of hypocrisy given his criticism of Brown back in 2007.

Seeking an immediate election could even counter the threat of a no-confidence vote in the House of Commons. If only a handful of Tory MPs opposed to a no-deal Brexit defect to the Liberal Democrats, Johnson will have no majority, even with the Democratic Unionist Party’s support.

Moreover, the arrival of a new prime minister tends to give his or her party a bounce in the polls. Labour, which has its own troubles, would be caught on the hop. And Johnson would start an election off the back of his leadership campaign. He would be warmed up for the fight.

If the Conservatives were to win a snap election, Johnson would have a mandate for his vision of Brexit. His personal authority would be very great. This would matter enormously if it were necessary for him to accept some kind of compromise with the EU before October. It would be equally important if Britain were to leave the EU without a deal.

Of course, any prospect of winning would hinge on Johnson being able to persuade a large number of people presently backing the Brexit Party to support him. Like so much in British politics at present, Johnson’s confidence in his ability to persuade is a matter of pure speculation.

Indeed, any talk of early elections is necessarily speculative. As Thatcher wrote in her memoirs: “Calling an election is a big decision and by constitutional convention is a matter for the prime minister alone.” Only Johnson knows his own mind – and maybe not even he.

Nicholas Allen, Reader in Politics, Royal Holloway.

This article first appeared on The Conversation.