Boris Johnson has said it was his "duty" to attend lockdown leaving drinks and claimed most of the Partygate rule-breaking in Sue Gray's report was "news to me".
The Prime Minister said he was "humbled" by the scandal and renewed his apology for attending his surprise birthday do in June 2020, for which he received a fine from the Metropolitan Police.
But he tried to wriggle out of censure for broader rule-breaking by claiming he didn't know about what was going on at many events in No10 and Whitehall.
The Whitehall enforcer's 37-page report laid bare the extent of the pandemic boozing, with red wine on the walls, vomiting, a fight, karaoke and attempts to conceal the rule-breaking.
Ms Gray said Boris Johnson must "bear responsibility" for what happened at the gatherings - eight of which he attended.
Speaking at a Downing Street press conference, the rattled PM insisted it was right to "say farewell to valued colleagues" at a string of leaving events investigated in Sue Gray's Partygate report.
He said: "When I was speaking to colleagues about the departure of a another spad [special advisor] or a Government advisor or official, it didn't occur to me that this was anything except what I felt was my duty to do as Prime Minister during a pandemic.
"That's why I did it. That's why I spoke as I did in the House of Commons."
He said he believed these were work events and added that "view appears to be substantiated by the fact that I wasn't fined for those events".
The police investigation into what occurred during a gathering in his Downing Street flat on November 13 showed that no rules were broken.
Ms Gray said in her report she had decided not to pursue an investigation into the "Abba party" held in the No 11 flat despite finding that alcohol was present on the evening Dominic Cummings was forced out of Downing Street.
He added: "On the Downing Street flat, what Sue says in her previous interim report is that the flat has a dual use.
"Historically, prime ministers have used it for meetings. The event in question was a work meeting and ... the Metropolitan Police did investigate and that was certainly the outcome of their investigation."
Mr Johnson suggested he had been unaware of the brazen boozing going on in Downing Street that Ms Gray's report uncovered.
But he dodged questions over whether staff involved would face disciplinary action.
He said: "A lot of the stuff that I saw in the report this morning was news to me.
"I think it's important that everybody who is in anyway involved in this sorry business has got to learn lessons and I think that applies to everyone named in the report."
Mr Johnson said the treatment of cleaners and security staff was "utterly unacceptable" after Ms Gray's said cleaners and custodians who uncovered law-breaking parties were left feeling "unable to raise properly" their concerns.
He said: "I was appalled to learn that there have been multiple examples in Sue Gray's phrase of disrespectful land and poor treatment of cleaning and security personnel.
"I personally apologised to those dedicated members of staff for what happened and I expect anyone who behaved in that way to do the same."
He said he had made inquiries to establish who had been rude to staff.
Asked if he ever considered resigning over Partygate, he said: "I overwhelmingly feel it is my duty to get on and deliver."
