The inquiry by Civil servant Sue Gray said the “senior leadership team ... must bear responsibility” for a culture that allowed events to take place that “should not have been allowed to happen”.
UK Prime Minister Boris Johnson has presided over a culture of lockdown-breaking parties that featured drunken fighting among staff, an inquiry revealed, prompting renewed calls for his resignation.
"Many of these events should not have been allowed to happen," the report by senior civil servant Sue Gray said on Wednesday.
"The senior leadership at the centre, both political and official, must bear responsibility for this culture," she wrote.
The report came out as a photograph published by the Daily Mirror newspaper showed a Downing Street table laden with wine bottles and doughnuts.
"I take full responsibility for everything that took place on my watch," he told MPs, in response to the long-awaited inquiry, insisting: "I am humbled and I have learned."
But Johnson said he was absent from most of the events, and denied ever lying to parliament.
He expressed hope that with the investigation now over, "we will be able to move on" in addressing priorities including the conflict in Ukraine and a spiralling cost-of-living crisis in Britain.
'Catalogue of criminality'
Gray released a preliminary version of her report in January but held off fuller publication as the Metropolitan police announced its own investigation. The Met is now under pressure to reopen the investigation as new evidence emerged this week.
Junior staffers who ended up fined by London's Metropolitan police, a majority of them women, had been told to attend events by their bosses, the report found.
Johnson is among dozens of people in Downing Street who have received police fines for breaching Covid regulations since 2020, and defied calls to resign after he received the fine.
But many MPs from his Conservative party were understood to be awaiting the details revealed in Gray's full report before deciding whether to trigger a leadership ballot.
The main opposition Labour party said the "catalogue of criminality" revealed by the report vindicated its calls for Johnson to quit, arguing he was more focused on "saving his own skin" than prioritising the public's needs.
Gray's report "provides definitive proof of how those within the building (Number 10) treated the sacrifices of the British people with utter contempt", Labour leader Keir Starmer told Johnson in the House of Commons.
"You cannot be a lawmaker and a law-breaker. It's time to pack his bags."