Bettors backed Keir Starmer to become the UK's next prime minister after the Metropolitan Police said around 20 fixed penalty notices would be issued to those who broke lockdown rules.
The Labour leader is 5.95/1 - a marginally shorter price than chancellor Rishi Sunak 6.05/1 - on who will occupy number ten Downing Street after Boris Johnson.
The Met said the first batch of fines would be for the most straightforward cases. This is not expected to include Johnson who denied he broke any rules.
Labour calls Johnson a liar
Labour has been quick to react to the breaking news.
Wes Streeting, the shadow health secretary, says the Met announcement about fines over Partygate showed Johnson was a "proven liar".
Labour has said Johnson must resign as prime minister if he is found to have broken rules and is fined by the police.
The Covid-19 Bereaved Families for Justice group responded to today's news by saying Johnson should have resigned months ago.
Two new markets have opened on the Exchange concerning Johnson's premiership - you bet on whether he will resign before the end of April and whether there will be a no confidence vote in his leadership the same month.
The partygate scandal punctured Johnson's popularity at the end of 2021 when the first reports of allegedly illegal parties in Downing Street during lockdown started to surface.
It raged into the New Year, with the PM appearing to be on the brink of leaving, but the pressure on Johnson eased off after Sue Gray's report into the allegations - even though it was damning - and the news agenda became dominated by the Russian invasion of Ukraine.
The price on Johnson leaving before September's Tory party conference drifted and he is still 1.261/4 to be PM by then.
The police fines, however, should put the partygate firmly back on the national agenda.
If you think there's a good chance Johnson will be out within the next six months then 3.814/5 on him not being PM by the time the conference comes around is an appealing price.
No overall majority is the favourite outcome at the next general election but the Conservatives are odds-on to win the most seats.
Keep up to date with the latest politics betting moves on our live blog.