An independent report into lockdown gatherings held at Boris Johnson's Downing Street office and residence is "excoriating" for the British prime minister and will make things "incredibly difficult" for him, the Times said.
Sue Gray, a senior civil servant, has been tasked with investigating the events and whether they broke lockdown rules set by Johnson. The publication of her report has been put on hold until the police complete their own inquiry.
Johnson has received one police fine and could be issued with more. An interim version of Gray's report said in January that "serious failures of leadership" led to alcohol-fuelled parties being held when social mixing was all but banned.
"Sue's report is excoriating," the Times newspaper quoted a senior official as saying.
"It will make things incredibly difficult for the prime minister. There's an immense amount of pressure on her — her report could be enough to end him. No official has ever been in a position like this before."
The Times said the report would be highly critical of Johnson, both for attending some of the events and for the office culture in Downing Street.
Johnson has apologised for the gatherings but said he did not realise at the time that he was breaching the restrictions as he thought he was attending work events. He has faced calls from opposition parties and some of his own lawmakers to quit.
Others have said they want to see the full report before deciding whether to submit a letter of no confidence in him. To mount a challenge to Johnson's leadership, 54 Conservative lawmakers must write letters to trigger a confidence vote.
Ministers have said the prime minister is focused on providing support to Ukraine and on helping people through a cost-of-living crisis, and that he does not need to resign.
Lawmakers in parliament agreed last week to hold a separate inquiry into whether Johnson misled parliament when he told lawmakers that the rules had been followed at all times.
(Reporting by Kate Holton; Editing by William Schomberg)