Twelve gatherings – including the PM’s birthday party – are being investigated by police, a report reveals.
Sue Gray has blamed a “failure of leadership” for allowing parties to take place in Downing Street when the country was under strict lockdown.
In long-awaited findings, the senior civil servant says some events “should not have been allowed to take place”.
And, she adds, “too little thought” was given to public health concerns and how it would look to the public.
The report does not contain direct criticism of Boris Johnson, who is due to face MPs at 1530 GMT.
Ms Gray investigated 16 separate gatherings – including three that were not previously known about.
Her report confirms that the Metropolitan Police is investigating 12 events for alleged Covid-rule breaking.
This includes the 20 May 2020 “bring your own booze” event in the Downing Street, which the PM has apologised for attending, and the PM’s birthday party on 19 June 2020.
Ms Gray’s statement says she has been “extremely limited” in how much she can say about the gatherings by the Met’s inquiries.
But she does make pointed criticisms of the culture in Downing Street among senior civil servants and staff.
“At least some of the gatherings in question represent a serious failure to observe not just the high standards expected of those working at the heart of government but also of the standards expected of the entire British population at the time.
“At times it seems there was too little thought given to what was happening across the country in considering the appropriateness of some of these gatherings, the risks they presented to public health and how they might appear to the public.
“There were failures of leadership and judgment by different parts of No 10 and the Cabinet Office at different times.
“Some of the events should not have been allowed to take place. Other events should not have been allowed to develop as they did.”
She adds that the “excessive consumption of alcohol is not appropriate in a professional workplace at any time”, likely to be a reference to reports of drunken behaviour in the Number 10 garden and staff filling a suitcase with bottles of wine.
Steps must be taken to ensure government departments have a “robust” policy on alcohol consumption, the report says.
Wait for findings
The report is crucial to Mr Johnson’s premiership, which has been rocked by weeks of damaging headlines about parties in Downing Street and other government buildings.
Many Conservative MPs have said they are waiting for its findings to decide whether to try to oust him from office.
At least 54 of them can set up a vote on his position if they submit letters of no confidence to a backbench committee representing Tory MPs.
Mr Johnson is due to address a meeting of all Conservative MPs after his Commons statement, as he seeks to rally their support.
The process was thrown into confusion last week, when the Metropolitan Police announced their own inquiry into an unspecified number of gatherings.
Ms Gray was forced to rewrite the report to be released on Monday after the force asked for only “minimal reference” to be made to events they are looking at, in order to “avoid any prejudice to our investigation”.
Asked whether a further version of Ms Gray’s report would be published after the police probe, the PM’s spokesman replied: “We will consider what will be appropriate in due course.”