UK Prime Minister Boris Johnson suffered two high-profile departures from his government on Tuesday, including that of his finance minister, in the first stirrings of a cabinet uprising after a slew of scandals.

Rishi Sunak quit as chancellor of the exchequer and Sajid Javid resigned as health secretary with both saying they could no longer tolerate the culture of scandal that has stalked Johnson for months.

Their resignations were announced minutes after the prime minister apologised for appointing a senior Conservative who quit last week after he was accused of drunkenly groping two men.

Days of shifting explanations followed the resignation of deputy chief whip Chris Pincher, with Downing Street initially denying Johnson knew of prior allegations against Pincher when appointing him in February.

But by Tuesday, that defence had collapsed after a former top civil servant said Johnson, as foreign minister, was told in 2019 about another incident involving his ally.

"I think it was a mistake and I apologise for it," the prime minister told reporters, after opposition MPs and some Tories accused him of lying over what he knew when he appointed Pincher. "In hindsight, it was the wrong thing to do."

The Pincher affair appears to have been the final straw for Sunak and Javid, coming after Johnson only narrowly survived a vote of no confidence among Conservative MPs a month ago.

In particular, the departure of the finance minister in the middle of policy differences over a cost-of-living crisis sweeping Britain is dismal news for Johnson.

In a caustic resignation letter, Sunak said "the public rightly expect government to be conducted properly, competently and seriously". He added: "I believe these standards are worth fighting for and that is why I am resigning."

Javid, who preceded Sunak at the Treasury before quitting over a prior bust-up with Johnson, wrote that the British public "expect integrity from their government".

The prime minister's survival in last month's no-confidence vote gave him the opportunity to show "humility, grip and new direction", Javid said.

"I regret to say, however, that it is clear to me that this situation will not change under your leadership – and you have therefore lost my confidence too." (AFP)