LONDON (AFP) - UK Prime Minister Boris Johnson on Thursday (May 26) apologised to Downing Street cleaners and security guards after an inquiry found they were abused by civil servants holding raucous, lockdown-busting parties.

Following Wednesday's release of the long-awaited report by senior bureaucrat Sue Gray, three more MPs from Johnson's Conservative party called publicly for his resignation.

But the Tory leader is refusing to quit, arguing that while he "bitterly" regretted the rule-breaking and ensuing police fines, he did not realise his own government's Covid-19 regulations were being breached and that it was time to move on.

In a series of lurid revelations made in her report, Ms Gray said Downing Street cleaners had to mop up spilt red wine. At least one reveller vomited, and two came to alcohol-fuelled blows.

The cleaners and security guards suffered "multiple examples of a lack of respect and poor treatment" from partying civil servants, Ms Gray found.

At his daily press briefing, Mr Johnson's official spokesman was forced to apologise himself after repeatedly insisting that no rules were broken at a time when Britain was in Covid-19 lockdowns over the past two years.

"He apologised to a number of staff yesterday. He spoke to more this morning. He was appalled by that behaviour," the spokesman said with regard to the security and cleaning staff.

Downing Street rules have already been changed to forbid in-office drinking except for social functions with outside guests, he said.

"I don't think we have the fridge anymore," the spokesman added, referring to a notorious wine cooler that was installed to facilitate the past partying.

Public anger

Opinion polls indicated deep public disapproval, with a snap survey on Wednesday finding three in five people think Mr Johnson should resign and three-quarters that he knowingly lied about "Partygate".

But outside an election, Conservative MPs are the only people able to force Mr Johnson from office.

He met late on Wednesday with Tory backbenchers, reportedly arguing that heavy-drinking predecessor Winston Churchill would not have been able to win World War II if Downing Street had imposed a total booze ban at the time.

A total of 19 Tory MPs have publicly called for Mr Johnson's resignation, but others are believed to be holding back due to the war in Ukraine.

Fifty-four letters of no-confidence are needed to trigger a leadership ballot.

Mr John Baron, one of the three MPs who came forward after the report's publication, accused Mr Johnson of misleading Parliament and said he "no longer enjoys my support".

The Prime Minister still faces a House of Commons inquiry into whether he deliberately misled MPs with his repeated denials of rule-breaking.

"The strong intent is to cooperate fully" with that inquiry, Mr Johnson's spokesman said.