What happens if the Prime Minister loses his seat?

Boris Johnson is defending a majority of 5,034 in Uxbridge and South Ruislip in Thursday’s election, the smallest of any sitting Prime Minister since 1924.

Pollsters have suggested the race could be close, so what happens if the Prime Minister fails to win a spot in the House of Commons?

According to one academic, Mr Johnson could remain in charge without a place in the Commons or the Lords because “there’s no constitutional bar to the PM not being a member of either House of Parliament”.

Robert Hazell, professor of politics at University College London, used the example of Sir Alec Douglas Home, who led the country from 1963-1964.

Prime Minister Boris Johnson during a visit to Gardiner Bros in Hardwicke, while on the General Election campaign trail (PA)

Sir Alec was a member of the House of Lords when he became prime minister but then relinquished his earldom.

In the 20 days between him leaving the Lords, and winning a by-election to gain his seat in the Commons, he was not a member of either House.

Prof Hazell said it is “harder to answer the question how politically acceptable that might be nowadays”.

“I’m talking about something that happened just over 50 years ago, in a more deferential age.”

If the Prime Minister does not win in his west London constituency, Prof Hazell thinks it likely that a Tory in a safe seat will be persuaded to stand down to allow Mr Johnson to stand in a by-election.

He explained: “I’m sure there would be loyal Tory MPs willing to stand aside if that enabled Boris Johnson then to swiftly get re-elected to the House of Commons.

“He might have to offer some inducement like a seat in the Lords.”

This scenario would become more complicated, however, in the case of a hung Parliament, as the Prime Minister would take on a caretaker role and would not be in a position to hand out public roles.

Prof Hazell continued: “The caretaker business complicates it further because there’s a caretaker convention which requires the caretaker PM not to initiate any new policy or make any major public appointments.”

Polling released on Monday projected that Mr Johnson will retain his Commons place.

YouGov’s MRP modelled that the Conservatives would win 49% of the vote in Uxbridge, compared to Labour on 40%.

However, the same data suggests that the Labour vote could be as high as 48%, and the Tory vote share as low as 41%.

Chris Curtis, political research manager at YouGov, said: “Our MRP model shows it’s unlikely we’ll see the Prime Minister lose his seat in the forthcoming General Election with Boris Johnson currently nine points ahead of his Labour rival in Uxbridge and South Ruislip.

“Even if Labour manage to aggressively squeeze what’s left of the Lib Dem vote, the Prime Minister should still be returned to his seat on December 13.”