According to Sue Gray's story, staff partied in Downing Street while the rest of the UK remained in lockdown, with their superiors' approval.
Many occurrences "should not have been allowed," according to the senior civil servant, and the PM and his officials "must accept responsibility for this culture."
The report details excessive drinking, staff illnesses, and mistreatment of cleaning and security personnel.
It claims that warnings concerning parties infringing Covid guidelines were ignored.
Boris Johnson told MPs that he accepted "full responsibility for everything that happened under my watch," that the experience had "humbled" him, and that he had learned lessons.
Ms Gray discovered the following in her 37-page report: Political and official leadership must bear responsibility for the culture at No 10
On the eve of Prince Philip's burial, staff partied till about 4 a.m.
In June 2020, there was another party "Some people consume excessive amounts of alcohol. One of the participants was ill. A brief altercation occurred between two other people."
To evade press photographers, a No 10 official sent a note referring to "drunkenness" and encouraging colleagues to leave No 10 via the rear exit following a December 2020 Christmas quiz.
"Numerous instances of disrespect and mistreatment of security and cleaning personnel"
Martin Reynolds, the PM's top adviser, was advised to cancel a "bring-your-own-booze" party planned for the Downing Street garden.
"The state or fact of being answerable, or accountable for something within one's power, control, or management," according to the dictionary definition.
So when the prime minister said he took "ultimate responsibility" for the events in Downing Street, some of his more suspicious MPs wondered if his following statements stood up to that billing.
He denied seeing the empty bottle-filled bins, the altercation, or the vomiting. Even when he was present and raised a glass at some of the contentious occasions, he was simply demonstrating "leadership" by wishing leaving employees well.
He'd left before any of the parties had even begun, and he had "no awareness of later procedures since I just wasn't there."
The public will not vote.
Mr Johnson met with five special advisors in his Downing Street residence with "food and alcohol" on the evening of Dominic Cummings' departure in November 2020, Ms Gray discovered.
The senior civil servant said that she had only gathered "minimal" information since she had only started gathering facts before the Metropolitan Police opened an investigation and had not…!