Johnson has faced repeated calls to resign from opposition politicians and some in his own party after it was revealed both he and officials had broken the rules that meant people could not socialise outside their households or even, in many cases, attend funerals for loved ones.

"I take full responsibility for everything that took place on my watch," Johnson told parliament on Wednesday.

The report by senior official Sue Gray did not specifically blame Johnson, but gave graphic details and included photographs from more than a dozen gatherings, some of which he attended.

Johnson was among those fined over a party to celebrate his 56th birthday on June 19, 2020, though Gray said he was unaware of the gathering in advance.

"Many of these events should not have been allowed to happen," the report said.

"The senior leadership at the centre, both political and official, must bear responsibility for this culture."

Johnson, who commissioned the report after revelations of boozy Downing Street events while social mixing was all but banned under stringent laws his government had made to curb the virus, said he was appalled by some of the behaviour it had uncovered.

"I ... am humbled and I have learned a lesson," he told parliament to jeers from the opposition benches.

Gray's interim findings were published in January, but most details were withheld until the end of a separate police inquiry, which concluded last week with 126 fines handed out.

Her full reports included emails and WhatsApp messages which showed many of the gatherings were planned in advance, with discussions on who would bring alcohol.

At one June 2020 event, Gray said there was "excessive alcohol consumption" that led to one person being sick and a fight between two others.

At another, held the night before the funeral for Prince Philip in April 2021, individuals partied into the early hours and damaged a swing.

"Many will be dismayed that behaviour of this kind took place on this scale at the heart of government," her report said.

"The public have a right to expect the very highest standards of behaviour in such places and clearly what happened fell well short of this."

For months, evidence of the alcohol-fuelled parties has dripped out into the media, forcing Johnson to apologise, change the team at his office and promise a reset to try to restore his authority.

Opposition Labour leader Keir Starmer said it was time for Johnson to quit.

The report laid bare "the rot that under this prime minister has spread... a government that believed that it was one rule for them and another rule for everyone else," he told parliament.

"You cannot be a lawmaker and a law-breaker."

Many Conservative lawmakers have become increasingly frustrated about having to defend their prime minister, but several said they would wait for Gray's full report before deciding whether to demand Johnson should quit.

Some felt the report was not as damning as it could have been.

"This is all so banal," one Conservative said on condition of anonymity, also pointing to Gray saying she was pleased progress was being made in addressing issues she had raised.

Johnson had initially denied there had been any parties or rule-breaking at Downing Street, and some lawmakers say his position is untenable if he is found to have lied to parliament, a matter under investigation by parliament's Committee of Privileges.

"I would like to correct for the record, to take this opportunity and not in any sense to absolve myself of responsibility, ... but simply to explain why I spoke as I did in this house," Johnson said, by way of apology for his earlier denials.

Ministers say he has not misled parliament, but one Conservative lawmaker said the details of the report suggested the prime minister had in fact done so.

"The question remains 'Did the PM knowingly mislead parliament?'," the second lawmaker said.

"Reading the report and its conclusions, it's very difficult to dispute that he did."

Australian Associated Press