Boris Johnson and Rishi Sunak are facing growing calls to resign after Downing Street confirmed both are being be fined by police.
It comes as the Metropolitan Police announced 30 additional fines on Tuesday in relation to Operation Hillman, which is looking into breaches of Covid-19 regulations at the top of government.
Mr Johnson is understood to have been present at six of the 12 events being investigated, but Downing Street confirmed his fine relates to his birthday party on June 19, 2020. It means he is the first sitting prime minister in history to break the law.
Meanwhile, the fine comes amid a torrid few days for Mr Sunak, who continues to face questions over his declaration on tax affairs.
So, what's next for the prime minister and Chancellor of the Exchequer?
How much will the fine be?
The prime minister and Ms Johnson both said they have paid their fines of £50 each.
Fines typically start at £100 for the first offence, but if they are paid within a 14-day period, the rate drops to £50. Fines grow to £200 for the second offence before doubling for each repeat offence, hitting the cap of £6,400.
It is unclear how much Mr Sunak has been fined, but he said on Tuesday night that he has paid the amount.
Could they have appealed the fine?
Any individual is entitled to appeal their fine, which could see them appear in court.
However, even if Mr Johnson or Mr Sunak felt the fines were unfair, they may have made a political decision not to take the case to court out of fear of how the public would perceive them.
There is also no guarantee their appeals would have been successful.
Does this mean Boris Johnson and Rishi Sunak have a criminal record?
A fixed penalty notice is not a criminal conviction, but it can be recorded on the Police National Computer - it is the equivalent to a minor speeding offence.
Could Boris Johnson lose his job now?
Mr Johnson will not automatically be removed from office - nor will Mr Sunak. The prime minister can, however, be voted out by his own MPs, according to Conservative party rules.
If Tories want to remove their party leader, they must submit a letter to the 1922 Committee chair outlining their aim.
If 15% of the party - under the current Parliament it would be 54 MPs - submit letters to the committee it will trigger a secret ballot, giving MPs the chance to back or boot the leader.
If more than 50% of Tory MPs then vote to remove him, he will lose his role of party leader and be barred from competing in the forthcoming leadership election.
If they win over half the votes, then they remain party leader and are given a year's immunity from any further confidence votes.
Only the Conservative party can remove Mr Johnson as prime minister. Other alternatives are for the PM to resign or for a general election, which isn’t due for two more years.
What about the Ministerial Code?
The prime minister's resignation could also be forced if he is found to have misled Parliament – on December 8 he told MPs in the House of Commons that he had been “repeatedly assured” no Covid rules were broken.
If it is decided he misled MPs, he would be obliged to resign according to Ministerial Code.
ITV News Political Editor Robert Peston writes that should Tory MPs keep the PM in power, without assessing how Parliament was misled, "then the charge will stick that this or any party with a big majority is simply an elected dictatorship, and the constitution means little or nothing".
What has Boris Johnson or Rishi Sunak said about the fine?
The prime minister and his wife Carrie Johnson both apologised after the fines had been confirmed. The PM added that the pair had both paid their £50 fines.
He said it “didn’t occur” to him that the birthday gathering on June 19 2020 was a violation of coronavirus rules. However, he said that, after being issued with the fine, he “now humbly accepts” he did breach Covid-19 laws.
In a statement, Mr Sunak offered a "unreserved apology" and signalled he would stay in his job.
"I understand that for figures in public office, the rules must be applied stringently in order to maintain public confidence," he said.
"I respect the decision that has been made and have paid the fine.
"I know people sacrificed a great deal during Covid, and they will find this situation upsetting. I deeply regret the frustration and anger caused and I am sorry.
"Like the prime minister, I am focused on delivering for the British people at this challenging time."