The Metropolitan Police has received new evidence from the Cabinet Office as it investigates reported breaches of Covid rules at Downing Street and Whitehall.
The force stressed that the new findings had not delayed the publication of the Sue Gray inquiry, the Mirror reports.
Ms Gray has been asked by the Met to make "minimal references" in her report to the parties officers are investigating in a bid to avoid prejudicing its inquiry.
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Scotland Yard is looking at "a number of events" in Downing Street and Whitehall during the pandemic - but the force has not specified which ones.
Reports have suggested it could be as many as eight gatherings.
Sue Gray's report had been expected this week but the timing has been thrown into chaos by the Met's bombshell announcement of a police probe on Tuesday.
The Whitehall inquiry is understood to be still ongoing but Ms Gray may be forced to decide whether to delay her report or strip out key details.
Opposition MPs blasted the appearance of an "establishment stitch-up" and a "Whitehall whitewash", which could buy Boris Johnson a reprieve.
In a statement on Friday, Scotland Yard said: "For the events the Met is investigating, we asked for minimal reference to be made in the Cabinet Office report.
"The Met did not ask for any limitations on other events in the report, or for the report to be delayed, but we have had ongoing contact with the Cabinet Office, including on the content of the report, to avoid any prejudice to our investigation."
However, some legal figures questioned why publishing the Whitehall report would prejudice the police investigation.
Nazir Afzal, a former chief Crown prosecutor for the North West, said on Twitter: "This is absolute nonsense from the Met Police.
"A purely factual report by Sue Gray cannot possibly prejudice a police investigation.
"They just have to follow the evidence, of which the report will be a part."
Top barrister Adam Wagner, who is an expert on Covid rules, tweeted: "I am not a criminal lawyer so perhaps I am missing something.
"How would a factual civil service report about events the police is investigating 'prejudice' their investigation?"
