Britain's embattled Prime Minister Boris Johnson is on Tuesday facing fresh allegations in the ongoing partygate scandal as details emerged of a surprise 56th birthday cake party, organised for him at the peak of the first COVID lockdown in June 2020. The scandal continues to spiral out ahead of an internal Cabinet Office inquiry report, which has now been delayed to an unspecified later date as Scotland Yard confirmed that the Metropolitan Police will investigate potential lockdown breaches related to alleged parties at Boris Johnson's office-residence at 10 Downing Street, as well as other government offices in London."As a result firstly of the information provided by the Cabinet Office inquiry team and secondly by the 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,” Met Police Commissioner Dame Cressida Dick told the London Assembly Police and Crime Committee at the Mayor of London's office.“I should stress that we are now investigating does not mean fixed penalty notices will necessarily be issued in every instance and to every person involved. We will not be giving a running commentary on our current investigations but I can assure you we will give updates at significant points," she said.Also Read | Lockdown party: Pressure mounts on UK PM Boris Johnson to resignThis criminal investigation, which could result in fines being issued on Downing Street and government officials, means that the internal Cabinet Office inquiry being led by top civil servant Sue Gray will deliver its report only after the police probe. UK Paymaster General Michael Ellis told the House of Commons that there is "ongoing contact" between the Met Police and Gray, who will meanwhile continue with her separate investigation. He said the government cannot comment on "what is an ongoing police investigation" and asked MPs "not to preempt its conclusions".Earlier, Downing Street said Johnson, who turned 56 on June 19, 2020, was present at an event "for less than 10 minutes" as his staff "gathered briefly" to wish him a happy birthday. The strict lockdown rules imposed at the time to contain the spread of coronavirus banned most indoor gatherings involving more than two people. But ITV News' reported on Monday night that up to 30 people attended the event, sang Happy Birthday and were served cake.The event reportedly took place in the Cabinet Room of Downing Street just after 2 pm local time that day and had been arranged as a surprise for Johnson by his then fiancee and now wife, Carrie Symonds, after he returned from an official trip to a school in Hertfordshire. "A group of staff working in Number 10 that day gathered briefly in the Cabinet Room after a meeting to wish the Prime Minister a happy birthday. He was there for less than 10 minutes," a Number 10 Downing Street spokesperson said.Also Read | Boris Johnson hit with dramatic defection, rebel plot over partygate scandalThe ITV report also claimed that the same evening, family friends were hosted upstairs in the Prime Minister's official residence in apparent breach of the rules. However, Number 10 denied that claim, "This is totally untrue. In line with the rules at the time the Prime Minister hosted a small number of family members outside that evening." A number of his ministers spoke out in his defence even as the rebellion among backbench MPs continued to mount."It obviously was the Prime Minister's birthday, he'd been given a cake earlier in the day, that's the picture in the newspapers," UK Transport Secretary Grant Shapps told Sky News'. “And he was clearly given a cake by staff when he got back to the office. These are staff he would have been working with and was working with all day long, and will have been many a time in the same room with them working on the response to coronavirus. They come in, give him a cake, I understand I think it lasted for 10 minutes and that was it," he said.The minister reiterated that it was ultimately for Gray to decide whether this was appropriate. "I think we can be pretty clear that the Prime Minister didn't present the cake to himself,” he added.Also Read | London Eye: UK confronts difference between a drinks event and a partyUK Culture Secretary Nadine Dorries said in a tweet, "So when people in an office buy a cake in the middle of the afternoon for someone else they are working in the office with and stop for 10 minutes to sing happy birthday and then go back to their desks, this is now called a party?" But Opposition Labour Party leader, Sir Keir Starmer, repeated his call for Johnson, 57, to resign in the wake of the latest revelations. “The Prime Minister is a national distraction and he's got to go," he said.It comes as Johnson meets his Cabinet for a regular weekly meeting on Tuesday amid the growing threat of war in Eastern Europe. A Conservative backbench rebellion against Boris Johnson's leadership is likely to continue intensifying.A total of 54 Tory MPs must write letters of no confidence in Johnson as a leader to Sir Graham Brady, chairman of the party's powerful backbench 1922 Committee, to trigger a leadership contest. Most were said to be waiting for the inquiry report to make up their minds, with the latest developments involving the police likely to renew their activities.