Around 30 people including Prime Minister Boris Johnson are being contacted by the Cabinet Office to warn them of the contents of the Sue Gray partygate report.
It is thought that most of the letters were sent out on Thursday, as the Metropolitan Police concluded its investigation into lockdown breaches in Downing Street and across Whitehall.
Mr Johnson is set to be among those approached by the Cabinet Office team but No 10 had no update as to whether he had received a letter on Friday evening.
It is understood the Prime Minister and Ms Gray held at least one meeting to update on the report’s progress while it was being drafted, but that its contents were not discussed at any point.
Such meetings would not have been viewed as unusual, a source said, with the aim to take stock of what stage the report was at.
Not everyone contacted by the Cabinet Office will necessarily be named or identified by some other means in the report – it may merely be that their actions are referenced because they are pertinent to the narrative of a particular event.
The investigators are understood not to be including the full details of the contents in the letters but instead are giving a “gist” of the relevant sections to those being approached.
Earlier, Mr Johnson insisted he would not seek to block names appearing in the senior civil servant’s report, and said he was “looking forward” to seeing its contents “pretty soon”.
The Prime Minister said he was “very grateful” for the Met’s investigation, which concluded with 126 fines.
There were demands for answers over how the PM escaped with just one fixed-penalty notice (FPN) despite being believed to have been present at multiple rule-breaking events.
Potentially damaging further details, including the names of some of those who attended gatherings, will be published in the Gray report.
Sources close to the investigation expect it will be published early next week.
On reports the PM had met with Ms Gray during the drafting process, a No 10 spokesperson said: “The Prime Minister commissioned the investigation led by Sue Gray and has been clear throughout that it should be completely independent.
“As he reiterated again today, the decision on what and when to publish rests entirely with the investigation team and he will respond in Parliament once it concludes.”
Mr Johnson declined to apologise again for the rule-breaking in No 10 during a visit to Hilltop Honey’s factory in Newtown in Powys, Wales, on Friday.
Asked if No 10 would be blocking any names from appearing in the report, he said: “That will be entirely up to Sue Gray and I’ll be looking forward very much to seeing what she has to say, and fingers crossed that will be pretty soon next week.”
Officials affected by the Gray inquiry, including those to be named, are being written to so they can have a chance to respond before the current draft is finalised for publication.
There were calls for Scotland Yard to explain how Mr Johnson received just the one fine, for his 56th birthday gathering in June 2020 when indoor mixing was banned.
Former director of public prosecutions Lord Ken Macdonald warned “it’s very difficult for us to disentangle exactly how the police investigation has proceeded and how fair it’s been”.
He told BBC Radio 4’s Today programme: “I think without the police providing an explanation for that it’s very difficult for us to understand why they came to the conclusions that they did.”
The crossbench peer said it was not known why the Prime Minister was fined for his presence at what was deemed one of the less serious events but not others.
There has also been no explanation as to why Cabinet Secretary Simon Case, who had to recuse himself from running the civil service inquiry after reports of a Cabinet Office Christmas party surfaced, has not been fined.
The Met declined to identify anyone in its £460,000 investigation.
A team of 12 detectives examined 345 documents, including emails, door logs, diary entries, witness statements and 204 questionnaires.
They also examined 510 photographs and CCTV images.
Mr Johnson, his wife Carrie Johnson and Chancellor Rishi Sunak were all fined over the birthday gathering.
But both Johnsons were told by police they face no further action, according to Downing Street, and Mr Sunak has not received an additional fine.
The Met said 28 individuals had received between two and five fines.