Rishi Sunak is facing growing unease in his party as a third Conservative MP resigned in 24 hours to trigger another by-election.

Nigel Adams, the MP for Selby and Ainsty, is an ally of Boris Johnson but did not link his resignation to that of the former PM who resigned last night, claiming he was being driven out of politics. Earlier, a fellow ally Nadine Dorries, quit the Commons.

The resignations have led to talk of civil war in the Conservative party as allies of Mr Johnson challenge the authority of Mr Sunak who is seen to be losing ground to Labour.

Mr Johnson’s statement that he is leaving Parliament “for now” has prompted speculation about a comeback but that seems unlikely to be in this parliament, despite suggestions he could fight either of the other two seats which are safer than his Uxbridge & South Ruislip constituency. 

The former Prime Minister spelled out his decision in a resignation letter that made clear his fury at a House of Commons investigation into whether he misled Parliament over Partygate.

It is understood that the Privileges Committee has ruled that he did mislead MPs and recommends he serve a ban from the Commons. The suspension would be long enough to trigger a by-election.

Mr Johnson chose to resign with immediate effect, accusing the committee of mounting a “witch-hunt” and describing it as a “kangaroo court”. He held a 7,000 majority at the last election.

He said the standards committee, led by Labour’s Harriet Harman but including Tory MPs, “have still not produced a shred of evidence that I knowingly or recklessly misled the Commons.”

In evidence given to the committee in March, Mr Johnson admitted misleading Parliament, but denied doing it on purpose.

In his statement, Mr Johnson turned on Mr Sunak, accusing the Prime Minister of betraying his legacy on a range of policies. He called for cuts to business and personal taxes and for the party to make the most of Brexit.

“We must not be afraid to be a properly Conservative government,” he said. “Our party needs urgently to recapture its sense of momentum and its belief in what this country can do.

“We need to show how we are making the most of Brexit and we need in the next months to be setting out a pro-growth and pro-investment agenda. We need to cut business and personal taxes — and not just as pre-election gimmicks — rather than endlessly putting them up.

“We need to deliver on the 2019 manifesto, which was endorsed by 14 million people. We should remember that more than 17 million voted for Brexit.”

While his resignation may have been sudden and dramatic, he indicated that he is planning to return to politics and said that he had left parliament only “for now at least”.

His decision to quit came hours after his Resignation Honours list was published, featuring some of his closest allies – including Priti Patel and Jacob Rees-Mogg – who have been rewarded with peerages.

Former secretaries of state Simon Clarke and Mr Rees-Mogg were knighted, while Ms Patel is made a dame.

No serving MPs were given peerages, avoiding by-elections. It had been thought Scotland Secretary Alister Jack would move to the Lords.

Former Conservative minister Nadine Dorries was not put forward for the House of Lords, despite speculation she would be on the published list.

Ms Dorries – who served as Culture Secretary under Mr Johnson – also stood down as an MP “with immediate effect” just over an hour before the honours list was released.

SNP Westminster Deputy Leader Mhairi Black said: “Boris Johnson has jumped before he was pushed, and no one in Scotland will be sorry to see the back of him.

“But he has also underlined the weakness of Rishi Sunak, who has no authority over the bitterly divided Tory party.

“Sunak has been utterly humiliated. On the day he was forced to accept Johnson’s dodgy honours list to shore up his position, his predecessor has stuck two fingers up at him and reminded everyone that Sunak was unable to take action for fear of a leadership challenge.