Boris Johnson is once again facing calls to resign after a leaked emailrevealed Downing Street staff were invited to a gathering in May 2020 at the height of lockdown.

The Prime Minister will face MPs amid furious demands to come clean over his attendance at a reported “bring your own booze” party in the No 10 garden in breach of Covid lockdown rules.

The disclosure triggered a new wave of public anger following the reports last year of parties in the run up to Christmas 2020, with Tory MPs openly warning Mr Johnson his position will be untenable if he has been shown to have lied.

Downing Street has refused to say if he was present at the May event, despite reports he and his fiancee (now wife), Carrie Symonds, were among around 30 people to attend at a time when such gatherings were banned.

HeraldScotland: Rules in England at the time of the alleged Downing Street party. (PA)Rules in England at the time of the alleged Downing Street party. (PA)

But as Boris Johnson faces fresh scrutiny, what happens if the Prime Minister was to resign?

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.