Boris Johnson has resigned as a member of parliament in a move widely seen as declaring war on Rishi Sunak.

His resignation triggers a by-election in Uxbridge and South Ruislip, a West London constituency where Boris had a majority of 7,210 and which the former prime minister would have found hard to defend in the general election expected next year.

Boris stepped down late on Friday night after being sent an advance copy of a report by the Commons privileges committee which informed him that it had found him guilty of deliberately “misleading” parliament over his Covid partygate statements.

In British politics deliberately misleading parliament is a resignation matter.

Boris’s defence has been that he had given wrong information to the Commons but he had not lied deliberately – and that he had corrected the record.

In a 1,000-word response, he attacked the privileges committee which has a Tory majority but is chaired by a Labour MP, Harriet Harman.

The I newspaper summed up the line that he was taking: “Boris Johnson declares war on Sunak as he quits parliament.”

In a comment piece, “War against Rishi”, the BBC’s political editor, Chris Mason, said: “The ghost of Boris Johnson haunts Rishi Sunak. It is the last thing the prime minister needs.”

There are many who think Boris jumped before he was pushed and that he is responsible for his own downfall but in his statement he revealed: “I have received a letter from the Privileges Committee making it clear – much to my amazement – that they are determined to use the proceedings against me to drive me out of Parliament.

“They have still not produced a shred of evidence that I knowingly or recklessly misled the Commons.”

He alleged that the committee’s “purpose from the beginning has been to find me guilty, regardless of the facts. This is the very definition of a kangaroo court.

“Sadly, as we saw in July last year, there are currently some Tory MPs who share that view. I am not alone in thinking that there is a witch hunt under way, to take revenge for Brexit and ultimately to reverse the 2016 referendum result.

“My removal is the necessary first step, and I believe there has been a concerted attempt to bring it about. I am afraid I no longer believe that it is any coincidence that Sue Gray – who investigated gatherings in Number 10 – is now the chief of staff designate of the Labour leader.”

Boris claimed: “I am now being forced out of Parliament by a tiny handful of people, with no evidence to back up their assertions, and without the approval even of Conservative party members, let alone the wider electorate.

“I believe that a dangerous and unsettling precedent is being set.”

Then he moved on to attacking Rishi: “When I left office last year, the government was only a handful of points behind in the polls. That gap has now massively widened.

“Just a few years after winning the biggest majority in almost half a century, that majority is now clearly at risk.

“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 must not be afraid to be a properly Conservative government.

“Why have we so passively abandoned the prospect of a Free Trade Deal with the US? Why have we junked measures to help people into housing or to scrap EU directives or to promote animal welfare?”

Boris threw out more than a hint that he intends to rise Phoenix like from the ashes: “It is very sad to be leaving Parliament – at least for now – but above all, I am bewildered and appalled that I can be forced out, anti-democratically, by a committee chaired and managed, by Harriet Harman, with such egregious bias.”

The phrase “at least for now” suggests he has not abandoned hope of standing again in a safer seat and returning one day as prime minister.

In his resignation honours list, Boris loyalists were rewarded. The former home secretary, Priti Patel, has been made a Dame. Another Indian, Kulveer Singh Ranger, a former director of transport while Boris was London mayor, has been given a peerage.