An inquiry into lockdown parties held in British Prime Minister Boris Johnson's Downing Street complex on Monday said some of the events should have been forbidden and identified leadership lapses.
Senior civil servant Sue Gray said she was limited in what she could say in her long-awaited report after London's Metropolitan police force launched its own probe.
But in the 12-page report made public, she decried "excessive consumption of alcohol" on various occasions in Downing Street, at a time when the British public was largely banned from socialising.
"There were failures of leadership and judgment by different parts of No 10 (Downing Street) and the Cabinet Office at different times," Gray wrote after investigating 16 separate gatherings.
"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 said.
The police are looking into 12 of the events, with the possibility that any of those attending, including Johnson, could be fined for breaching Covid regulations in force over the past two years.
The prime minister has faced demands to resign over the "partygate" revelations. He was due to give a statement in parliament at 1530 GMT in response to Gray's findings.