Boris Johnson is facing brazen calls for his resignation from his own backbenchers as he awaits the outcome of a potentially bombshell report being prepared by a senior official.

The Prime Minister apologised on Wednesday for attending a “bring your own booze” party in the Downing Street garden in May 2020, when the rest of the country was in lockdown.

The PM insisted he thought the party was work-related, but said he recognised “with hindsight I should have sent everyone back inside”.

He said an inquiry headed by senior official Sue Gray was examining the situation but accepted “there were things we simply did not get right and I must take responsibility”.

But as Boris Johnson faces fresh scrutiny, what happens if the Prime Minister was to resign and who would replace him?

Here is all you need to know.

What happens if a Prime Minister resigns in the UK?

This will depend on the situation.

If a Prime Minister loses a general election they will offer their resignation to the monarch who will then invite the winning party to form a new government in their name.

However, if a Prime Minister resigns while their government is still in power, the process differs.

In this case, the government is still elected and therefore the resignation of the standing prime minister triggers a leadership contest, where fellow members of the government will campaign to be leader of the party.

When the leadership contest is decided, the outgoing Prime Minister will go and offer their resignation to the Queen, and advise she appoints the new leader of the party as prime minister. 

This new prime minister is not then required to hold a general election, but they often choose to soon after they take over. 

Has a UK Prime Minister resigned before?

Yes, it happens quite regularly.

When Tony Blair announced his resignation on May 10 2007, he triggered a Labour leadership contest. 

Gordon Brown received 313 nominations for leader, and his only opponent, John McDonnell, soon conceded defeat. 

On June 27 2007, Brown officially became prime minister of the UK. 

The same thing happened with David Cameron's resignation on June 24 following the Brexit vote.

Theresa May won the Conservative leadership contest after her being left the sole candidate. 

When May then announced she would resign on June 7 2019, another leadership contest was triggered, resulting in the election of Boris Johnson over Jeremy Hunt. 

Who would replace Boris Johnson if he resigned?

If Boris Johnson was to resign and a Conservative leadership election was held it seems chancellor Rishi Sunak would be in pole position to take lead and in turn become Prime Minister. 

While not neccessarily a gurenteed winner, Sunak would be in with a good chance.

Foreign secretary and equalities minister Lizz Truss would be another senior contender given her popularity within the party.

The Betfair Exchange confrims as much with the two currently clear favourites to win leadership should Boris Johnson resign. 

Full list of odds: 

  • Rishi Sunak 15/8
  • Liz Truss 11/4
  • Michael Gove 6/1
  • Jeremy Hunt 8/1
  • Priti Patel, Sajid Javid, Oliver Dowden 14/1
  • Tom Tugendhat, Penny Mordaunt 16/1

Mr Johnson’s press secretary insisted that he was not a liar and “he is not resigning”, but dismissed as “hypothetical” questions over whether that could change after Ms Gray’s report was published.