Boris Johnson will face MPs following the Metropolitan Police’s conclusion that coronavirus laws were broken at the heart of his government.

Downing Street has insisted Mr Johnson did not mislead Parliament when he claimed rules were followed, despite Scotland Yard deciding to issue an initial 20 fines after its investigation into events in No 10 and Whitehall.

Mr Johnson is likely to face a difficult session of Prime Minister’s Questions and he will then endure a further grilling from senior MPs at the Liaison Committee.

The Prime Minister and his allies had an indication of public anger about the situation at a party for Tory MPs in London on Tuesday night, where bereaved relatives of Covid-19 victims heckled senior Conservatives.

Dozens of grief-stricken relatives who lost loved ones during the pandemic lined up outside the entrance of the Park Plaza hotel, across Westminster Bridge from the House of Commons, to boo guests as they arrived.

Shouts of “shame on you” and “off to another party are we?” were directed at Levelling Up Secretary Michael Gove and Brexit opportunities minister Jacob Rees-Mogg as they turned up to the venue.

The public may never know who in government is issued with a fixed-penalty notice (FPN), as Scotland Yard said they would remain anonymous – although Downing Street has promised to confirm if the Prime Minister or Cabinet Secretary Simon Case are among those hit with a fine.

The decision to issue FPNs means the police believe the law was broken – with more fines expected to follow as officers continue to sift through evidence.

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.

The Met on Tuesday said it would begin referring 20 cases to the Acro Criminal Records Office, which is responsible for issuing the penalties.

The Prime Minister’s official spokesman refused to say whether Mr Johnson would quit if he was fined.

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”.

Any sackings or resignations among No 10 aides would put pressure on Mr Johnson to follow suit if he too was found to have broken the law.

The Prime Minister’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 Met would not say how many individuals will get a fine – it is possible some will get more than one if they attended multiple illegal events.

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.

Prominent critic Andrew Bridgen told the PA news agency that a “day of reckoning” may come in regard to the partygate scandal, but not at this moment in time.

Mr Bridgen, who has withdrawn the letter of no confidence in the PM that he submitted to the Tory 1922 Committee, said he would back Mr Johnson if there was a vote on his future “otherwise we’d be playing into the hands of Mr (Vladimir) Putin”.

While Mr Johnson may be safe from being ousted by Tory critics for the moment, he still faces an uncertain future if the Met does conclude he personally broke the law.

A cessation of hostilities in Ukraine, however unlikely that may appear, could remove one of the reasons for Conservatives to offer support to Mr Johnson, while a poor showing in May’s local elections would heap further pressure on him.

The cost-of-living crisis, set to be exacerbated by rising energy bills and the national insurance hike in April, will also add to Mr Johnson’s difficulties.

Both Ukraine and the economic pressures facing households will feature in the questions posed to Mr Johnson by the Liaison Committee, a panel made up of senior MPs.

His session with the panel, made up of the chairs of Commons select committees, follows his weekly showdown with Sir Keir Starmer at Prime Minister’s Questions.