Watch excruciating exchange as Boris Johnson dodges Partygate questions 17 times
The first 20 fines will be issued following the Partygate scandal – but police have not named the individuals involved.
The Metropolitan Police said that the ACRO Criminal Records Office would be responsible for issuing the penalties. It is expected that further fines could be handed out as evidence mounts up.
The force is looking into at least 12 events, six of which Boris Johnson is thought to have attended. The Met has not confirmed how many people will receive fines, but some could face several if they attended more than one event. While unconfirmed, the penalties can range between £100 and £10,000; they are subject to the law at that time, the person's role and the size of the gathering.
The prime minister faced immense pressure to quit after the scandal, but the international crisis in Ukraine has turned their attention. However, the Met's intervention confirmed it believes laws were broken, which could reignite the debate about Johnson's leadership.
Government minister Will Quince said the gatherings "shouldn't have happened", but it would be "inappropriate" to comment further.
"I completely understand the considerable upset caused, the events that took place shouldn't have happened," he told Sky News.
"But I hope you'll understand that both as an education minister but more importantly, as there's an ongoing live Metropolitan Police investigation, it's just not appropriate that I comment."
He said questions over whether the prime minister should resign if fined were "hypothetical" and said Johnson had committed to publishing a full report by senior official Sue Gray into the scandal "as soon as the Metropolitan Police have concluded their investigation".
Quince added: "Looking at the moment over in Ukraine, and even worse over in Russia, I think it's a brilliant thing that we have a free press in this country that is able to ask these kinds of questions."
Deputy Labour leader Angela Rayner said that the war in Ukraine should not be a reason to save Johnson's back.
"After over two months of police time, 12 parties investigated and over a hundred people questioned under caution, Boris Johnson's Downing Street has been found guilty of breaking the law," she said.
"The culture is set from the very top. The buck stops with the Prime Minister, who spent months lying to the British public, which is why he has got to go."
"It is disgraceful that while the rest of the country followed their rules, Boris Johnson's government acted like they didn't apply to them.
"This has been a slap in the face of the millions of people who made huge sacrifices."
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