Boris Johnson is under renewed pressure after Downing Street admitted staff gathered inside No 10 during the first Covid lockdown to mark his birthday.

ITV News reported that up to 30 people attended the June 2020 event, sang Happy Birthday and were served cake.

No 10 said staff had "gathered briefly" to "wish the prime minister a happy birthday", adding that he had been there "for less than 10 minutes".

But a number of MPs have expressed criticism over this latest revelation.

Rules at the time - on 19 June 2020 - banned most indoor gatherings involving more than two people.

ITV News said the birthday event had taken place in the Cabinet Room just after 14:00 BST that day, adding that it had been arranged as a surprise for Mr Johnson by his then fiancee, Carrie Symonds, after he returned from an official trip to a school in Hertfordshire.

As well as No 10 staff, the interior designer Lulu Lytle attended, having been in Downing Street working on the refurbishment of the PM's flat.

And a source told the BBC that Chancellor Rishi Sunak was also in the room, but had arrived at the end to attend a meeting, rather than being invited.

Transport Secretary Grant Shapps told the BBC the event was not organised by Mrs Johnson but by the PM's own office, who "thought they were being kind" by marking his birthday.

Other ministers disputed the detail, with Environment Secretary George Eustice denying 30 people had gathered in the Cabinet Room, saying the number of staff present was "closer to 10" and it "was literally just a birthday cake brought in at the end of the day".

Mr Shapps, whose father was in hospital for four months during the pandemic, also denied as many as 30 had been present, telling BBC Breakfast the group had been working together all day.

But he later told BBC Radio 4's Today programme the gathering had been "unwise given the circumstances".

However, despite his "own anger and frustration", Mr Shapps asked for "patience" whilst waiting for the investigation into parties in No 10 during lockdown - lead by senior civil servant Sue Gray - to be published, adding: "You won't have to wait long."

The BBC has learned that Ms Gray, already knew about the 19 June event.

Her findings are expected to be published later this week.

Downing Street is accepting that this gathering/event/party/whatever you want to call it did take place.

But this marks a new stage in how the government is handling these accusations.

We started with the denials, which didn't work because they weren't strictly accurate.

Then we got the government acknowledging public anger, but that didn't really get them anywhere.

Then we had the stonewalling of "wait for Sue Gray".

But now No 10 are being a little bit more muscular in how they address these things, trying to put out their own version of the facts.

And what has happened in the last 24 hours points towards what the strategy for dealing with the Sue Gray report might be.

But putting out their interpretation, their version, will be balanced on the other side of the ledger with people pointing out the precise rules, potential failures of judgement by the people involved and just the sheer emotional weight of it.

And that is the significance of this party story. Everyone had multiple birthdays during this pandemic so everyone can compare and contrast their experience with that of the prime minister's.

Some MPs and senior figures in the Tory party have denounced the latest revelations, while many continue to wait for Ms Gray's findings before making a judgement.

Members from across the Commons have also pointed out the contradiction of the PM's own actions to a letter he sent to the then-seven-year-old Josephine Booth, consoling and praising her after she cancelled her own birthday party in March 2020 due to coronavirus restrictions.

Labour's shadow foreign secretary David Lammy said Mr Johnson should reflect on his ability to live by the rules he made himself, while Labour leader Sir Keir Starmer repeated his call for Boris Johnson to stand down, saying: "The prime minister is a national distraction and he's got to go."

Former Conservative Party chair Baroness Warsi told the BBC News Channel it was time for Mr Johnson to "think long and hard about what is in the best interest of this country".

"The question he should be asking himself every morning is, 'Is me staying in office allowing me to run this office in a way in which is making the country better, or am I a distraction?'" she added.