Boris Johnson is facing increasing pressure to resign after he was fined as part of a police probe into allegations of lockdown parties held in Downing Street.

       Downing Street last week confirmed that the Prime Minister's fixed penalty noticed (FPN) is linked to his "birthday party" in the Cabinet room in June 2020.

       Carrie Johnson, the wife of the Prime Minister, also received a fixed-penalty notice (FPN), her spokeswoman confirmed.

       Could this mean that the Prime Minister has to resign? Here we answer your questions:

       What laws were broken?

       Different 'partygate' events broke different laws given the rapidly changing nature of Covid restrictions during the pandemic.

       The Prime Minister’s surprise birthday celebration broke the rule in place at the time banning gatherings of more than two people inside.

       Meanwhile, the leaving party for two No 10 employees in Jan 2021 broke the rule banning individuals from meeting people socially with anyone outside of their household.

       How much will the Prime Minister have to pay?

       Fines for breaching Covid lockdown restrictions have ranged from ￡50 to ￡10,000, depending on the breach and how long it takes the recipient to pay.

       The first batch of FPNs issued by the Met to Downing Street staff last month were ￡50.

       However, for members of the public the fines originally started at ￡60, but were reduced to ￡30 if paid within 14 days. Second-time offenders could be fined ￡120, with this doubling for further offences.

       But by the latter stages of the pandemic fines were increased to ￡200, reduced to ￡100 if paid within 14 days.

       What happens now?

       Boris Johnson could still be issued further fines if the Met Police find that he attended other illegal gatherings. He will then have the option to challenge those fines on an individual basis in court should he see fit.

       Politically, the Prime Minister could face a challenge to his leadership if Sir Graham Brady, the chairman of the 1922 committee, starts to receive letters calling for a vote of confidence.

       If 54 letters are received, a vote would be triggered for when Parliament returns after Easter recess. If Mr Johnson loses then a leadership election would take place.

       Does he have a criminal record?

       No. A fixed penalty notice is an administrative alternative to prosecution which does not appear on a criminal record. If left unpaid and if the Prime Minister loses his appeal, it can amount to a criminal offence.

       Has any other PM ever done something similar?

       Mr Johnson is the first known Prime Minister to have broken the law whilst in office, and the first who is known to have received a fixed penalty notice.

       When was the last time a PM was involved in a criminal investigation?

       When Sir Tony Blair was in No 10 he was questioned by police – but not under caution – over cash-for-honours allegations.

       In July 2007 the former prime minister, who was questioned three times by officers, welcomed the decision not to prosecute anyone over the claims.

       The police probe into the alleged sale of peerages ended in an announcement from the Crown Prosecution Service that there was insufficient evidence against anyone to secure a conviction in court.

       Who has already called for the PM to resign?

       Dozens of politicians have already seized the opportunity to call on Boris Johnson to resign, including Sir Keir Starmer and Nicola Sturgeon.

       Sir Keir said: "Boris Johnson and Rishi Sunak have broken the law and repeatedly lied to the British public. They must both resign. The Conservatives are totally unfit to govern. Britain deserves better."

       Nicola Sturgeon, the Scottish First Minister, tweeted: "Boris Johnson must resign. He broke the law and repeatedly lied to parliament about it."

       Mayor of London Sadiq Khan also called for Boris Johnson's resignation. "A Prime Minister who breaks the laws his Government makes and then lies about it isn't fit for office," he said.

       Others to issue the calls include David Lammy, the shadow foreign secretary; Ian Blackford, the SNP Westminster leader; and Sir Ed Davey, the Liberal Democrat leader.

       This article is kept updated with the latest information.