More photographs showing Boris Johnson drinking at rules-busting lockdown gatherings in No 10 are expected to be published in Sue Gray's report into Partygate.
Sources close to the investigation said officials had to "push very hard internally" for the damning images to be included.
The Mirror understands that photos of the Prime Minister at his Downing Street birthday party holding a can of Estrella beer will be revealed.
One insider claimed the picture was "more incriminating" than that of Lee Cain's leaving do as it undermined claims it was an impromptu gathering ahead of a Covid meeting.
It is believed to identify Mr Johnson, Chancellor Rishi Sunak - both of whom were fined over the event - and Cabinet Secretary Simon Case - who was not.
The image was taken by Downing Street's official taxpayer-funded photographer who was documenting the event in June 2020.
Downing Street insiders also believe that Ms Gray could publish photos of the leaving do for two No 10 private secretaries where Mr Johnson made a speech.
They claimed that multiple pictures were taken at the boozy event on 14 January, 2021, including of the PM with drinks.
Angry attendees at the event in the depths of lockdown were stunned to find that they were fined but Mr Johnson was not.
One said: "Everybody is furious that loads of people in the room got fined but him and nobody can figure out why, because there's all these photos of him with booze."
Another added: "Very many people at the gathering have been fined, and they were virtually all civil servants.
"You've got to wonder how the political people, the special advisors who were there, managed to get away with it.
"Did people answer the questions in different ways?
"It just feels wrong that people who did what they were told to do and were open and transparent were fined yet those who were less so weren't."
Ms Gray, whose long-awaited report is expected to be published as early as today, handed more than 300 images to Scotland Yard from her probe.
Downing Street insiders claimed the PM was "quite happy" for images to be published to dispel the public belief that Downing Street was "like Ibiza on a Saturday night".
It comes after photographs emerged showing Mr Johnson raising a glass of fizz at a leaving bash for former spin doctor Lee Cain.
The photos, leaked to ITV News, threaten to derail the PM's rigorous efforts to move on from the scandal.
Angry insiders also claimed that others at the leaving drinks received fixed penalty notices for the event - while the PM escaped without another fine.
They emerged just hours after former No 10 aide Dominic Cummings - an arch enemy of Mr Johnson - claimed pictures would be published imminently.
Mr Cummings, referring to photographic evidence held by officials, said: "One of the consequences is that I expect photos of the PM will emerge very quickly, within the next 24-48 hours.
"Any reasonable person looking at some of these photos will only be able to conclude that the PM obviously lied to the Commons, and possibly to the cops, and there is no reasonable story for how others were fined for event X but not him."
