Staff No10 were stunned that Boris Johnson denied knowing about rule-breaking parties

Boris Johnson faces a day of reckoning over the Partygate scandal as Whitehall enforcer Sue Gray prepares to finally release her report tomorrow.

The Prime Minister is accused of lying to Parliament over its multiple claims that “no rules were broken” in No10 during lockdown.

Downing Street staff revealed they looked on in disbelief as Mr Johnson repeatedly told the Commons he was unaware of the gatherings, which were breaking the rules.

One said: “We watched it all live and just looked at each other in disbelief like – why?

“Why is he in denial when we were with him the whole time, we knew the rules were being broken, we knew those parties were happening?”

The government has been plagued by the scandal since the Mirror first reported last year that No10 was hosting social events while the rest of the country stuck to strict Covid lockdown rules.

Tonight, Mr Johnson faced new claims that he had condoned illegal social gatherings by “getting a glass for himself” rather than disrupting regular events.

His own office organized get-togethers – like the BYOB party in the garden – and his executives even sent out email invitations.

Insiders told the BBC’s Panorama how the Prime Minister himself set the culture by suggesting he “wanted to be liked” and that staff should be able to “let their hair down”.

One suggested they felt they had the Prime Minister’s permission to socialize, even though it meant breaking the rules because “he was there”.

They said: “He wasn’t there and said that this shouldn’t happen.

“He didn’t say, ‘Can everyone break up and go home? Can everyone social distance? Can everyone put on masks?’

“No, he didn’t tell anyone. He grabbed a glass for himself.”

They revealed how staff at gatherings “sat on each other’s laps” and even “stayed over the night” after going into the wee hours.

They suggested that with the Prime Minister’s apparent blessing, regular drinks sessions – “pinned in the diary at least every week” – should be held.

The Mirror was told in January that it had encouraged aid workers to “let off steam” on Wine Time Fridays, despite the ban on indoor socializing.

A source said: “Boris used to stop by to chat while they had a drink.

It was on the way to his apartment and the door was normally open. He knew about it and encouraged it.”

Another added: “He could see everyone sitting there drinking as he walked up to him.

“He came in and said, ‘Hello, everyone’s had a rough week? Let off some steam? Oh cool’.

“The idea that he didn’t know drinks existed is total nonsense. When the PM tells you to ‘let off steam,’ he’s basically saying that’s fine.”

But the drinking wasn’t limited to Fridays and staff reported that they often turned up at work at No. 10 to find what they described as “a mess”!

One added: “There were bottles, empties, rubbish – in the bin but overflowing – or indeed left on the table at times.”

The Mirror was also told that Downing Street security – known as caretakers – have been forced to warn staff about parties.

A source claimed they sent an email reminder to the building in the summer of 2020. Another suggested stopping by to speak to people directly.

An insider told the BBC how one of the janitors was mocked as they tried to stop a party in full swing.

“I remember when a janitor tried to stop it all and he just shook his head at that party and was like, ‘This shouldn’t be happening,'” he said.

“People made fun of him because he was so excited that this party was happening and wasn’t supposed to be happening.

“Then how did it happen when the rest of the country was living under strict lockdown?”

Mr Johnson, who is expected to make a statement to the House of Commons after Ms Gray released her report before asking Tory MPs to back off on the affair, is facing renewed threats from angry backbenchers.

Senior Tory Tom Tugendhat admitted: “To be honest it’s very difficult to have faith in the government at the moment”.

But Downing Street faces more questions about the Partygate scandal after a new picture emerged of yet another boozy Lockdown No10 session.

Pictured is a table strewn with bottles of soda and wine at the last press conference held by Senior Adjutant James Slack on November 17, 2020.

The event, which sources say 30 to 40 staff attended, is not believed to have been investigated by Ms Gray or Scotland Yard.

It was sent to aid workers on a WhatsApp group in response to a message from a senior official who wrote: “Time to open the Covid security bar”.

Earlier in the afternoon, No. 10 officers exchanged messages that appeared to show the event was planned in advance.

Bomber photos followed of the Prime Minister raising a glass in a separate exit after explicitly denying in the House of Commons that the event ever happened. Downing Street today had to deny that the Prime Minister had asked Ms Gray to drop plans to publish her report.

He reportedly hinted at a meeting with her earlier this month that there was no longer any point in publishing her findings as the facts were “all out there”. However, No 10 has refused to release minutes of the “secret” meeting, insisting it would remain private.

The Mirror can reveal that senior staff No10 has sent multiple emails to Ms Gray and her team over the past 24 hours.

They appear to be showing what one insider described as “getting their story straight” at the gathering.

Downing Street sources claimed it was common practice to let them know what they wanted to say – and then get their reply.

But it risks undermining the Prime Minister’s claim that Ms Gray’s report is independent of Downing Street despite being her boss.

Ms Gray’s account of the failure of leadership at the heart of government during the pandemic is expected to be damning.

Sources told the Mirror that more “incriminating” photos showing the Prime Minister drinking at rule-breaking lockdown gatherings at No 10 are expected to be included. Some close to the probe said officials would have to “push very hard internally” for the damning pictures to be taken.

London Mayor Sadiq Khan asked the Met to explain why the Prime Minister only received a single fine while others received fines for attending the same events.

Scotland Yard handed 126 fines to 83 people over the Partygate scandal and a handful of senior staff lost their jobs, but the Prime Minister remains in office.

A No 10 spokesman added tonight: ‘As part of their investigation, the Cabinet Office team was able to speak to No 10 staffers to establish the facts of what happened at the time. Both she and the Met Police had access to all information relevant to their investigation, including photographs.

“The Met has completed its investigation and Sue Gray will be issuing her report shortly, after which the PM will address Parliament in full.”