Boris Johnson is facing questions about No 10 parties from MPs, as the results of an internal inquiry into possible lockdown breaches are due.
Angry exchanges are likely at Prime Minister’s Questions, with senior official Sue Gray’s report expected to be delivered later.
The Met Police has also announced its own investigation, heaping more pressure on the prime minister.
And Foreign Secretary Liz Truss has urged a “change in culture” in No 10.
She told BBC Breakfast there were “clearly concerning reports” over parties and it was important to “fix the issues”, adding: “But that shouldn’t diminish the fantastic work that has been done under this government and this prime minister.”
The BBC understands that Ms Gray has not sent her report to the prime minister yet, but it is still expected that this will happen at some point during Wednesday.
Mr Johnson has apologised for attending a “bring-your-own-booze” event on in the No 10 garden 20 May 2020, during the first lockdown, saying he thought it was a “work event”.
Met Police Commissioner Cressida Dick said on Tuesday that the force was looking into potential breaches of Covid laws at a number of events in government buildings since 2020.
Such investigations were carried out in cases of the “most serious and flagrant breach” of regulations, or when it was considered those involved “ought to have known that what they were doing was an offence”, she added.
Sue Gray is keen, I’m told, that the inquiry is published in its entirety with no summary, or redactions which could blur or mask some of its more pointed information.
The report is said to be full and frank, and is not expected to be easy reading either for the government, or the civil service itself.
It’s understood that there has been no shortage of evidence, with photographs and WhatsApp messages passed to her.
Much of that evidence has over recent days been passed to the police, explaining why the Met concluded that it was important for them to publicly announce that they would also investigate.
This adds to concerns for Mr Johnson over the gatherings, with Labour, the Liberal Democrats and the SNP continuing their calls for him to resign.
Some Conservative MPs have also demanded he go, but many others say they are waiting for the Gray report before deciding whether to submit letters of no confidence in Mr Johnson, potentially triggering a leadership contest.
At least 54 Tory MPs must write to Sir Graham Brady, chairman of the backbench 1922 Committee, to set up a vote on the prime minister’s future.
Mr Johnson has pledged to make a statement in the Commons after the report is made public, but there has been no official confirmation of when it will be published.
There is also doubt about how much of Ms Gray’s findings will be made public and how much time, if any, opposition political parties will get to scrutinise them before the prime minister speaks in Parliament and faces their questions.
Labour and the SNP have asked the government for assurances they will get advance notice.
“The government should not seek to hide” any information contained in the Gray report, shadow education secretary Bridget Phillipson told the BBC News Channel.
“The prime minister is taking the British people for fools if he thinks they can’t see what’s going on,” she added.
But House of Commons Leader Jacob Rees-Mogg said: “The government will behave entirely properly in terms of any statement, and the usual courtesies are extended to the opposition.”
The cabinet was in “unanimous support” of the prime minister, because “anyone who did not support the prime minister would be obligated to resign”, he added.
Mr Johnson has said he welcomes the Met investigation and that it will “give the public the clarity it needs” over the allegations.
His spokesman said the prime minister did not believe he had broken the law.
Timeline: The alleged government gatherings
The government is facing mounting pressure over several events that are alleged to have been held during lockdowns. Here is what we know about them and the restrictions in place at the time:
Boris Johnson announced a plan to take the “first careful steps” out of the lockdown that began in March 2020. But he said people should continue to “obey the rules on social distancing and to enforce those rules we will increase the fines for the small minority who break them”.
Legal restrictions at the time said you could not leave your house without a reasonable excuse and government guidance was that you could meet one person outside of your household in an outdoor setting while exercising.
A photo from May 2020 showed the prime minister and his staff with bottles of wine and a cheeseboard in the Downing Street garden. When asked about it, Boris Johnson said, “those people were at work talking about work”.
About 100 people were invited by email to “socially distanced drinks in the No 10 garden” on behalf of the prime minister’s principal private secretary, Martin Reynolds.
Witnesses told the BBC the PM and his wife were among about 30 people who attended.
Boris Johnson has confirmed he attended the event, saying he was there for 25 minutes and “believed implicitly that this was a work event”.
On Boris Johnson’s birthday, up to 30 people gathered in the Cabinet Room at No 10 to present the prime minister with a birthday cake and sing Happy Birthday, according to a report by ITV News.
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”.
Rules at the time banned most indoor gatherings involving more than two people.
Boris Johnson announced plans for a “significant return to normality” in England by Christmas “through targeted, local action” instead of national lockdowns.
But he added that the timetable relied on “every one of us staying alert and acting responsibly”.
With cases of coronavirus rising again, the prime minister told people in England that “we are once again asking you to stay at home” as a new national lockdown began.
He said people should only leave their homes “for work if you can’t work from home, for education, and for essential activities and emergencies”. Indoor gatherings with other households were banned, unless they were for work purposes.
Sources told the BBC that Downing Street staff members attended a gathering with Carrie Johnson in the flat where she and the prime minister live. A spokesman for Mrs Johnson denies the party took place.
A leaving event was held for No 10 aide, Cleo Watson, where people were drinking, and Mr Johnson made a speech, according to sources.
The second national lockdown ended after four weeks but Boris Johnson replaced those restrictions with “tough tiers to keep this virus down”.
London was placed in tier two, which banned two or more people from different households from meeting indoors, unless “reasonably necessary” for work purposes.
The Department for Education has confirmed it had an office gathering to thank staff for their work during the pandemic. It says drinks and snacks were brought by those who attended and no outside guests or support staff were invited.
The Conservative Party has admitted that an “unauthorised gathering” took place at its HQ in Westminster. It was held by the team of the party’s London-mayoral candidate, Shaun Bailey, who has since stepped down as chair of the London Assembly police and crime committee. The Metropolitan Police is to speak to two people who attended the party.
Multiple sources have told the BBC there was a Christmas quiz for No 10 staff last year. A photo – published by the Sunday Mirror – showed Boris Johnson taking part and sitting between two colleagues in No 10. Mr Johnson has denied any wrongdoing.
London moved into the highest tier of restrictions and Matt Hancock, who was health secretary at the time, said it was important “everyone is cautious” ahead of the festive period.
The Department for Transport apologised after confirming reports of a party in its offices that day, calling it “inappropriate” and an “error of judgment” by staff.
A leaving party was held at the Cabinet Office for the outgoing head of the civil service Covid taskforce – the team responsible for drawing up coronavirus restrictions.
Kate Josephs, now chief executive of Sheffield City Council, apologised for the event, saying she was “truly sorry that I did this and for the anger that people will feel as a result”.
Downing Street originally denied a report by the Daily Mirror that a party took place in Downing Street.
However, a video obtained by ITV News showed the prime minister’s then-press secretary Allegra Stratton, joking about reports of an event, saying: “This fictional party was a business meeting and it was not socially distanced.”
Lockdown restrictions were eased in England, with pubs and restaurants allowed to reopen with outdoor service only.
However, working from home continued to be recommended and socialising indoors with people from other households was not allowed. Meeting others outdoors was limited to groups of six people or two households.
Two parties were held by Downing Street staff at No 10, the night before Prince Philip’s funeral.
One of the events was a leaving party for the PM’s then director of communications James Slack, who has apologised for the event and acknowledged it “should not have happened at the time that it did”.
Boris Johnson was not at either party.