Conservative lawmaker Jeremy Wright, a former British minister and attorney general, said on Monday he believed Prime Minister Boris Johnson had damaged the government's authority and should resign.
He joins several of Johnson's lawmakers who have withdrawn their support for the British leader since a damning official report published last week detailed a series of illegal parties at his Downing Street office during Covid-19 lockdowns.
Wright said he found it impossible to accept Johnson did not bear some personal responsibility for setting the tone in Downing Street, which he said had shown a "routine disregard for the spirit, and often the letter of the Covid rules".
"I fear too that these events have done real and lasting damage to the reputation not just of this government but to the institutions and authority of government more generally," Wright said in a statement.
Wright said restoring accountability and faith in good government required more than apologies, and Johnson remaining in office would hinder crucial government objectives.
"I have therefore, with regret, concluded that, for the good of this and future governments, the prime minister should resign," he said.
More than 20 Conservative lawmakers have publicly called for Johnson to quit since the reports of lockdown-breaking parties began to steadily drip into the media. At least 54 are required to formally request a confidence vote for one to be triggered.