Britain's main opposition leader on Sunday accused Prime Minister Boris Johnson of breaking the law after a bruising series of revelations about lockdown-breaching parties.

In the latest, Johnson's wife Carrie was photographed on the front page of the Sunday Telegraph newspaper embracing a friend at a September 2020 party, in apparent violation of the then rules on social distancing.

At least six lawmakers in Johnson's Conservative party have now called publicly for him to quit, while others say they are awaiting the findings of an internal inquiry by senior civil servant Sue Gray.

Labour leader Keir Starmer, who is enjoying an opinion poll surge on the back of the Downing Street "partygate" allegations, said the facts were already clear.

"I think he broke the law. I think he's as good as admitted that he broke the law," Starmer told BBC television. Gray only has the remit to establish the facts, he added, calling for the police to look into a possible criminal inquiry once her report is out.

"The prime minister has degraded the office of prime minister and he has lost full authority not only in his own party, but in the country," Starmer said.

After weeks of denials and stonewalling, Johnson this week apologised in parliament for at least one boozy event organised by his staff which he attended in May 2020, when Britons were banned from socialising.