Boris Johnson is fighting for his political future after MPs investigating his partygate denials denounced the “flimsy” assurances they were based on.

In at times short-tempered testimony lasting more than three hours, the former prime minister insisted there was not a “shred of evidence” to show he lied to MPs.

It would have been “utterly insane” for him to have misled Parliament, he told the Privileges Committee that could recommend his suspension from the Commons.

I think that Boris Johnson is finished anyway

If a proposal for a 10-day suspension is voted through by MPs, a by-election in Mr Johnson’s seat could be triggered, potentially spelling the end of his parliamentary career.

Arch-loyalist Jacob Rees-Mogg said Mr Johnson won public support with his defences despite them being met with exasperation by multiple members of the cross-party panel of MPs grilling him.

The Tory MP told Channel 4 News: “I think that if Boris Johnson went to a by-election he would win it comfortably. Because I think he’s winning in the court of public opinion, who see this as a kangaroo court.”

Mr Johnson declined to repeat such attacks against the inquiry by some of his supporters but hit out at the “manifestly unfair” process.

He appeared to argue that the committee’s fairness would be proved if he was exonerated of any wrongdoing.

He accepted he misled MPs but said he did not do so “recklessly”, insisting he denied lockdown breaches “in good faith” on the advice of officials, who turned out to be wrong.

Harriet Harman, the Labour chairwoman of the Tory-majority committee, asked whether he could see why they were “a bit dismayed about the flimsy nature” of the assurances.

Senior Tory Sir Bernard Jenkin questioned why Mr Johnson failed to take “proper advice”, which Mr Johnson angrily rejected as “complete nonsense”.

Mr Johnson also hit out at Alberto Costa for raising a “completely ridiculous assessment” after the Conservative suggested his reliance on advisers was a “deflection mechanism”.

The ex-prime minister also suffered a blow when he saw his rebellion against his successor Rishi Sunak’s new Brexit arrangements for Northern Ireland fail.

He took a break from the committee hearing to vote against a key plank of the Windsor Framework but was joined by only 21 Tory rebel MPs, meaning it passed comfortably.

Mr Johnson indicated he could refuse to accept the inquiry’s verdict if it finds he committed a contempt of Parliament by deliberately misleading the Commons, saying he would “wait to see”.

The remark was echoed by Conservative Party chairman Greg Hands when asked if the committee was being fair to Mr Johnson.

“We’ll have to wait and see,” he told ITV1’s Peston. “I think it’s impossible to judge that until we see the report.”

Senior Tory MP Caroline Nokes predicted any hopes Mr Johnson might have of a return to Downing Street are futile.

Asked whether he is finished if he is punished, she told Peston: “I think that Boris Johnson is finished anyway.”

A campaign group representing families bereaved in the pandemic accused Mr Johnson of deflecting and blaming everyone but himself.

Lobby Akinnola, from Covid-19 Bereaved Families for Justice, told BBC Newsnight: “A fair question is, does he need to be advised to tell the truth? And I think secondly, does he need advice to follow his own rules that he set?”