Boris Johnson did not mislead MPs when he told them no lockdown rules had been broken in Downing Street, No 10 has insisted, despite the Metropolitan Police concluding the law was breached.

Investigators will begin handing out 20 fines over parties and gatherings held across Whitehall during Covid measures, the Met said on Tuesday.

The imminent issuing of the fixed penalty notices (FPNs) means the police have ruled the law was broken – with more fines expected to follow as officers continue to sift through evidence.

But No 10 has denied the Prime Minister misled the House of Commons when he defended the goings-on in his home and workplace.

Mr Johnson is not thought to be among those set to receive a fine at this stage – despite it being understood that he was present at six of the at least 12 events being probed – as he is contesting the allegations and took advice from his personal lawyer on how to respond.

His official spokesman said Downing Street had not been informed by the Met that Mr Johnson is among those referred to the ACRO Criminal Records Office, which is responsible for issuing the penalties.

“We’ve said we’ll update if that were to occur but our position has not changed,” he said.

He refused to be drawn on whether Mr Johnson would resign if he did get a fine.

He also declined to say whether fined individuals can carry on working in No 10, though former chief whip Mark Harper suggested law-breaking civil servants or special advisers would have to be sacked.

In a tweet, the Tory MP posted a screenshot of the Civil Service Code, highlighting a passage saying they must “comply with the law”.

The identities of those fined will not be disclosed by Scotland Yard.

Downing Street said it will confirm if Mr Johnson or Cabinet Secretary Simon Case is issued with a FPN, but not if anyone else in Downing Street is fined.

No 10 staff will not need to come forward if they get a FPN, but they will be asked to update their vetting information depending on their security clearance.

The PM’s spokesman said Mr Johnson was not misleading on the numerous occasions he defended the saga, despite wrongdoing now being confirmed.

“At all times, he has set out his understanding of events,” he said.

“The Prime Minister has apologised to the House already.”

He added: “You can expect to hear more from the Prime Minister when the investigation is concluded and Sue Gray has set out her report.”

Ms Gray is the senior civil servant tasked with investigating the allegations of lockdown-busting gatherings and has not yet been able to release her full findings.

The Cabinet Office said it would not be appropriate to comment on the first 20 partygate fines while the police probe is ongoing.

The Met would not say how many individuals will get a fine – it is possible some will get more than one if they attended more than one event.

The force would also not say which parties the fines relate to.

Mr Johnson came under intense pressure to quit as a result of partygate, but in recent weeks the war in Ukraine has seen Tory MPs rally round their leader.

But the Met’s intervention, confirming it believes laws were broken at the heart of Government, could reignite the debate about his leadership.

Hannah Brady, spokeswoman for Covid-19 Bereaved Families for Justice, said the PM’s team had “regularly and blatantly” broken “the same rules that families across the country stuck with even when they suffered terribly as a consequence”.

The group will today mark a year since they began to draw hearts on the national Covid memorial wall in London, and Ms Brady – whose father Shaun died at 55 after contracting Covid – said: “It’s crystal clear now that whilst the British public rose to the challenge of making enormous sacrifices to protect their loved ones and their communities, those at 10 Downing Street failed.

“Frankly, bereaved families have seen enough. The PM should have resigned months ago over this. By dragging it out longer all he is doing is pouring more salt on the wounds of those who have already suffered so much.”

Government minister Will Quince earlier told Sky News the gatherings “shouldn’t have happened”.

He said questions over whether Mr Johnson should resign if fined were “hypothetical”, but 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 the war should not be used as an excuse to save Mr Johnson.

“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.”

Liberal Democrat leader Sir Ed Davey said: “If Boris Johnson thinks he can get away with partygate by paying expensive lawyers and throwing junior staff to the wolves, he is wrong.”

More than 100 questionnaires were sent out to people at the gatherings, including the PM and the Chancellor Rishi Sunak.

The events included a “bring your own booze” gathering in May 2020 and a surprise get-together for Mr Johnson’s birthday in June 2020.

In January, Ms Gray published a partial report, which said there were “failures of leadership and judgment” in parts of No 10 and the Cabinet Office.

The initial publication contained limited detail due to the police investigation. A fuller report is expected once the Met’s inquiry ends.