Publication of the document had been delayed after the Metropolitan Police announced it was launching an inquiry into the allegations, but an interim version in January was published.
And now the police inquiry into Partygate is finished with 126 fixed penalty notices issued, the way is clear for the report to be revealed in full.
Around 30 people, including Boris Johnson, are being contacted by the Cabinet Office to warn them of the contents of the report ahead of its publication.
However, there is increasing speculation the Cabinet Secretary Simon Case will come under pressure to resign due to conclusions made in the report. But who is Simon Case, and why would the report’s findings prompt his resignation? Here’s what you need to know.
Who is Simon Case?
Simon Case is the Cabinet Secretary and head of the home civil service.
In December last year the Prime Minister appointed him to lead the inquiry into allegations of Christmas parties at Westminister during lockdown.
However just one week later he had to recuse himself from the inquiry due to reports a party had taken place in his private office.
A day later the 43-year-old resigned from the inquiry, and the role was taken over by civil servant Sue Gray.
At the time No 10 said Mr Case had removed himself from the process “to ensure the ongoing investigation retains public confidence”
It was reported the do had been organised by a private secretary in Mr Case’s team, and that it was included in digital calendars as: “Christmas party!” and included an online quiz.
The Cabinet Office said Mr Case played no part in the event, “but walked through the team’s office on the way to his own office”, and he avoided receiving a fine.
Is Simon Case expected to resign and why?
It is expected Mr Case will come under pressure to resign as a result of the findings.
The Metro reports that Whitehall officials believe he is set to take the blame.
The news site also reports a senior figure says Ms Gray’s report could be even more damaging for the Prime Minister than the fine he was given in April for attending his birthday party.
As the UK’s most senior civil servant, Mr Case is expected to be heavily criticised in the report, and it is thought he will be forced to offer his resignation as a result, or be sacked by Mr Johnson.
Meanwhile the Telegraph reports a source as saying Mr Case would come in for some “stinging criticism” over his role in events and said: “He knew about what was going on and as the head of the civil service, the ultimate responsibility was his.”
When will Sue Gray report be published?
The report is expected this week, though the exact date is not known.
On Monday Mr Johnson told reporters at a school in south-east London “it can’t be long now” before the report is out.
According to reports publication is expected before MPs break for a 10-day recess on Thursday evening.