Scotland Yard has launched an investigation into potential breaches of coronavirus laws at a “number of events” in Downing Street and Whitehall.

Metropolitan Police Commissioner Dame Cressida Dick said on Tuesday officers were now investigating potential offences over two years after being passed information from the Sue Gray inquiry.

The move plunges Boris Johnson into deeper jeopardy ahead of the publication of the investigation by Ms Gray, a senior civil servant in the Cabinet Office.

The department did not immediately confirm reports suggesting the report will be further delayed pending the police investigation.

Dame Cressida told the London Assembly’s Police and Crime Committee: “What I can tell you this morning is that as a result of the information provided by the Cabinet Office inquiry team and, secondly, my officers’ own assessment, I can confirm that the Met is now investigating a number of events that took place at Downing Street and Whitehall in the last two years in relation to potential breaches of Covid-19 regulations.”

She pledged to only give updates at “significant points” and declined to say which alleged parties are under investigation, nor would she put a timeline on when officers could detail their findings.

“The fact that we are now investigating does not, of course, mean that fixed penalty notices will necessarily be issued in every instance and to every person involved,” she said.

Dame Cressida said investigations are carried out into “the most serious and flagrant type of breach” where individuals knew they were committing an offence or “ought to have known”.

She said “several other events” that appeared to have taken place in Downing Street and Whitehall had also been assessed, but they were not thought to have reached the threshold for criminal investigation.

A further delay to the long-awaited publication of Ms Gray’s inquiry will prolong the saga when Mr Johnson and others in the Tory party want it concluded.

A Cabinet Office spokesman said: “The investigation being carried out by Sue Gray is continuing.

“There is ongoing contact with the Metropolitan Police Service.”

Deputy Labour leader Angela Rayner questioned how Mr Johnson can remain Prime Minister with Downing Street under police investigation.

“Boris Johnson is a national distraction. Conservative MPs should stop propping him up and he should finally do the decent thing and resign,” she added.

Commons Leader Jacob Rees-Mogg sought to defend the Prime Minister’s record after the police investigation was launched, saying he was “honoured to be under his leadership”.

After leaving a Cabinet meeting, he told reporters in Downing Street: “The leadership of Boris Johnson this country has had has been so brilliant – that he has got us through this incredibly difficult period and he’s got all the big decisions right.”

The Met had been under pressure to launch an investigation for weeks, with the Daily Mirror first reporting allegations of parties in No 10 during Covid restrictions two months ago.

Fresh allegations have emerged at a steady pace since then and have now totalled at least 19 separate events.

The latest emerged on Monday when Downing Street was forced to admit Mr Johnson had a birthday celebration inside No 10 during the first lockdown.

Downing Street conceded staff “gathered briefly” in the Cabinet Room following a meeting, after it was alleged 30 people attended and shared cake despite social mixing indoors being banned.

ITV News reported the Prime Minister’s wife, Carrie Johnson, had organised the surprise get-together complete with a chorus of “happy birthday” on the afternoon of June 19 2020.

Interior designer Lulu Lytle admitted attending but insisted she was only present “briefly” while waiting to talk to Mr Johnson about the lavish refurbishments she was carrying out to the couple’s flat above No 11.

Chancellor Rishi Sunak was understood to have briefly attended as the gathering was breaking up as he entered the room to attend a Covid strategy meeting.

ITV reported picnic food from M&S was eaten and Martin Reynolds, Mr Johnson’s under-fire principal private secretary, was also said to have attended, as was No 10’s director of communications Jack Doyle and head of operations Shelley Williams-Walker.

Social gatherings indoors were forbidden under lockdown laws at the time, with a relaxation of the regulations permitting gatherings of up to six people to take place outside.