UK Prime Minister Boris Johnson's approval ratings have slumped since "partygate" allegations related to his breach of coronavirus restrictions in 2020 emerged last month.

Johnson's fate appears to lie in the hands of senior civil servant Sue Gray, whom he has commissioned to look into the May 2020 event and other Downing Street gatherings that year.
Johnson's fate appears to lie in the hands of senior civil servant Sue Gray, whom he has commissioned to look into the May 2020 event and other Downing Street gatherings that year. (Reuters)

UK Prime Minister Boris Johnson is fighting for his political future as his Conservatives descended into open internal warfare after he belatedly apologised for attending a party during the coronavirus lockdown.

Most cabinet members rallied around Johnson after his mea culpa on Thursday, but the backing given by some such as Rishi Sunak, his powerful finance minister and potential successor, was distinctly lukewarm.

The apparent breach of coronavirus restrictions has enraged the public, who were forced to abide by rules that prevented them from visiting sick and dying loved ones, or attending funerals.

While expressing "heartfelt apologies", Johnson on Wednesday sparked ridicule by saying he had believed the May 2020 gathering was a work event.

READ MORE: Boris Johnson sorry for attending lockdown party, deflects calls to resign

'No longer tenable'

Douglas Ross, the Conservatives' leader in Scotland, joined at least four Tory backbench MPs in calling for Johnson to quit after the prime minister admitted joining the party in his Downing Street garden in May 2020, when Britain was under a strict lockdown.

"Regretfully, I have to say his position is no longer tenable," Ross told STV.

Cabinet member Jacob Rees-Mogg dismissed Ross as a "lightweight" Tory figure, sparking rebukes from other MPs and warnings that the upper-crust Englishman was bolstering the case for Scottish independence.

Northern Ireland Secretary Brandon Lewis insisted Johnson had been "very, very sincere" in his apology, amid warnings that Conservative MPs could be mobilising for a no-confidence vote.

On Wednesday, Labour leader Keir Starmer for the first time joined other opposition chiefs in demanding that Johnson resign.

One new poll by YouGov in The Times newspaper gave Labour a 10-point lead over the Tories, its biggest margin since 2013, and said six out of 10 voters believe Johnson should resign.

READ MORE: PM Johnson faces fresh scandal over UK government's lockdown breach

READ MORE: UK PM Johnson's Conservatives suffer shock by-election defeat

Source: TRTWorld and agencies