Boris Johnson’s chief of staff had a quick look at Sue Gray’s report and made changes, it has been claimed.
Two insiders told the Mirror that the document was reviewed before publication by Steve Barclay, who reportedly asked for changes.
They said the section covering a rally in the Downing Street flat was “edited out” on Tuesday evening.
The government has denied the allegations, also raised in the Commons.
Senior civil servant Ms Gray published her damning report in Partygate on Wednesday after the Met Police investigation concluded.
She revealed startling details of drunken parties, fights, vomiting and laughter from security guards.
Mr Johnson told MPs he had been ‘humbled’ by the scandal – in which he was fined for breaking Covid laws – but refused to step down.
He is facing a growing Tory rebellion with MPs submitting letters to try to trigger a vote of no confidence.
A third source claimed that the passage regarding the apartment had been changed, but they did not know by whom.
The Prime Minister denied that he or his political team had seen the report earlier or asked for changes.
No10 added: “The Prime Minister and his political team saw the report for the first time on Wednesday morning.
“No part of the report has been altered by #10.”
Today Labor MP Angela Eagle asked the Commons whether Mr Barclay had been told about the report early.
Separately, Downing Street admitted that an official had seen parts of the document before it was published.
Mr Johnson denies claims he asked Ms Gray to table her report at a private meeting this month.
The release led to further questions after she appeared she dropped her probe in a boozy ‘Abba party’ at the Downing Street flat on November 13, 2020.
Ms Gray said it was not ‘appropriate or proportionate’ to continue the ‘limited’ progress she made after the Met launched its investigation.
The Prime Minister’s wife Carrie, later joined by her husband, reportedly sang The Winner Takes It All to advisers after spin doctor Dominic Cummings quit.
The allegations were denied by Ms Johnson’s spokeswoman.
It comes as Mr Johnson’s spokesman apologized for not telling the truth about the No10 parties.
Meanwhile, the Met’s Chief Constable is under pressure to explain how Mr Johnson, who also apologised, ‘got away with it’ with a single fine.
Acting Commissioner Sir Stephen House said he did not believe there was ‘clear evidence’ that the Prime Minister had repeatedly broken the rules.
The Met investigated six events Mr Johnson attended and fined others who attended, but the Tory boss escaped further punishment.
Sir Stephen said officers were not swayed by the fact that they held Mr Johnson’s fate in their own hands.
London Mayor Sadiq Khan demanded an explanation of the force’s decisions.
Mr Johnson is facing fresh calls to step down from three other MPs – John Baron, David Simmons and Stephen Hammond.
More than 20 letters have been submitted to trigger a vote of no confidence, but 54 are needed.