Asked at Prime Minister's Questions by fellow Conservative Tim Loughton if there were "any circumstances in which he should resign", Mr Johnson said he would if he "felt it was impossible.. to go on" as a government.

But he added: "The job of a prime minister in difficult circumstances when he has been handed a colossal mandate is to keep going, and that's what I am going to do."

Politics Hub: Sajid Javid delivers damning speech after quitting

The resignations began after Number 10 admitted Mr Johnson had known about allegations of inappropriate behaviour against disgraced former deputy chief whip Chris Pincher, dating back to 2019, before hiring him, despite sending out ministers to say he did not know any specifics.

Mr Pincher resigned last week after further allegations that he groped two men at a private club in London, and he was later suspended from the Conservative Party.

Former senior civil servant Lord McDonald revealed on Tuesday that the PM had been told in person of the 2019 allegations, despite what Downing Street was telling the press.

Less than 12 hours later, Rishi Sunak resigned as chancellor and Sajid Javid quit as health secretary, prompting a flurry of more junior ministers saying they could no longer support Mr Johnson.

Sir Keir Starmer attacked the PM over his handling of the scandal, reading out the accusations levelled at Mr Pincher as a "reminder to all those propping up this prime minister just how serious the situation is".

In fiery exchanges at PMQs, the Labour leader said the list of resignations had left him with a "z list cast of nodding dogs" on his frontbench.

But he said having failed to quit during all the other scandals to hit Mr Johnson's government, even those departing did not have "a shred of integrity", adding the "sinking ships [are] fleeing the rat".

It was not just opposition MPs putting the boot in, with several on the Conservative benches using PMQs to tell Mr Johnson to go.

Gary Sambrook - an executive member of the 1922 committee of Tory backbenchers, which could be instrumental in the PM's future - said Mr Johnson "constantly tries to deflect from the issue, always tries to blame other people for mistakes, and [there is] nothing left for him to do than take responsibility and resign."

David Davis, who called for the PM to go six months ago, reiterated his demand, saying he needed to "do the honourable thing [and] put the interests of the nation before his own interests and before, in his own words, it does become impossible for government to do its job".

But Mr Johnson insisted: "It's exactly when times are tough, that when the country faces pressures on the economy and pressures on their budgets and when we have the biggest war in Europe for 80 years, that is exactly the moment that you'd expect a government to continue with its work, not to walk away, and to get on with the job."

After PMQs, Number 10 also said Mr Johnson would fight any fresh vote of confidence in him by backbenchers, and he believed he still had the support of the majority of his MPs.