British Prime Minister Boris Johnson and Finance Minister Rishi Sunak will be fined for breaching COVID-19 lockdown laws in what has become known as the "Partygate" scandal, prompting calls on Tuesday for their resignation.

Johnson's wife Carrie will also be fined, as the political storm following revelations of a swathe of lockdown-busting parties in and around Downing Street threatens to engulf Johnson once more.

"The prime minister and chancellor of the exchequer have today received notification that the Metropolitan Police intend to issue them with fixed penalty notices," a Downing Street spokesperson said on Tuesday.

The announcement came after London's Metropolitan Police said they had issued more than 50 fines to the parties, without disclosing the number or identities of those being fined.

The leader of the opposition Labour Party, Keir Starmer, swiftly called for the two most senior members of the government to resign.

"Boris Johnson and Rishi Sunak have broken the law and repeatedly lied to the British public," Starmer tweeted.

"They must both resign. The Conservatives are unfit to govern. Britain deserves better."

Johnson's office said his fine was for attending a surprise birthday gathering in his honor on the afternoon of June 19, 2020, in the Cabinet Room at Number 10.

Carrie Johnson and Sunak were reportedly both also at the gathering, but it was not immediately clear if their fines were for the same event.

Johnson was left fighting for his political survival earlier this year after several lawmakers from his ruling Conservative Party withdrew their support for his leadership over the affair.

Many Conservative MPs have submitted letters calling for a no-confidence vote in Johnson's leadership.

If the Conservative Party's 1922 Committee receives such letters from 54 of Johnson's 360 MPs, it will spark a confidence vote.

The leader of the opposition Liberal Democrats, Ed Davey, called for parliament to be recalled from its Easter recess for a confidence vote.

"This is a government in crisis neglecting a country in crisis," Davey tweeted.

Russia's invasion of Ukraine had eased the political pressure on Johnson over the scandal. Conservative MP Roger Gale said on Tuesday that now was not the time to "unseat" the prime minister, which would bolster President Vladimir Putin.

"It's serious, of course," Gale said.

"But ... I am not prepared to give Vladimir Putin the comfort of thinking that we are about to unseat the prime minister of the United Kingdom and destabilize the coalition against Putin.

"So any reaction to this is going to have to wait until we have dealt with the main crisis which is Ukraine and the Donbas," he said, referring to the eastern Ukrainian region where Moscow is now concentrating its assault.

Bereaved families of the COVID-19 pandemic victims also called on Johnson to resign.

Lobby Akinnola, the spokesperson for COVID-19 Bereaved Families for Justice, said Johnson and Sunak "broke the law" and "took us all for mugs.

"There is simply no way either the prime minister or chancellor can continue ... Their dishonesty has caused untold hurt to the bereaved," he said.

"They have lost all credibility with the wider public, which could cost lives if new variants mean restrictions are needed in the future."

London police are still investigating claims that Johnson and government officials organized and attended at least a dozen boozy events in 2020 and 2021 that violated Britain's then-strict virus curbs.

Johnson has already apologized for the parties, which included Christmas celebrations and a drink-fuelled gathering the evening before Prince Philip's funeral.

The prime minister initially denied any rule-breaking events had occurred in the complex where he lives and works, and he consistently rejected any suggestion of personal wrongdoing.

But his opponents accused him of having misled Parliament by insisting the Downing Street events were work-related and within the rules.