A birthday celebration for Boris Johnson where a Cabinet minister suggested he was “ambushed with cake” will form part of the Metropolitan Police’s inquiry into alleged gatherings across Whitehall.

The gathering on June 19 2020, could also bring Chancellor Rishi Sunak into the saga, as he was understood to have briefly attended the Cabinet Room where aides wished the Prime Minister a happy birthday.

Northern Ireland minister Conor Burns previously defended the PM amid reports his wife Carrie had organised a surprise birthday get together which 30 people attended.

He told Channel 4 News “he was, in a sense, ambushed with a cake”, but later told The Telegraph’s Chopper’s Politics podcast: “I’m told under some authority, indeed from him, that there actually wasn’t a cake.”

A resurfaced article from The Times the day after the gathering suggested there had been cake – and it was decorated with a Union Jack pattern.

The extent to which the gathering was a party will now be probed by officers.

ITV, which first reported on the birthday gathering, said 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.

Some 12 events are being investigated by the Met, with the birthday gathering one of at least four directly linked to the Prime Minister.

The others are the May 20 2020 gathering in the Downing street garden which Mr Johnson has admitted he briefly attended, and two alleged events on November 13, with a party reportedly held in the flat Mr and Mrs Johnson share.

Mr Johnson was also reported to have delivered a leaving speech for Lee Cain, his departing director of communications, at an alleged gathering on the same evening.

On Friday, No 10 said it could not comment on whether there was cake at the birthday celebration until the partygate investigations had concluded.

A spokesman for Mr Johnson said: “You will know what we said earlier this week on the matter, that a small number of staff briefly came into the Cabinet room on the PM’s birthday.

“Beyond that I can’t comment further ahead of any conclusion of the investigation.

“As you’re aware, there’s an independent investigation ongoing by Sue Gray in the Cabinet Office.

“I can only point you back to what we said earlier this week.”