BORIS Johnson has refused to accept the devastating conclusion of a Commons committee that he is a serial liar, calling it “rubbish” and “deranged”.

The former Prime Minister also accused the Tory-majority group of MPs led by Labour veteran Harriet Harman of lying.

He called the committee “beneath contempt” and claimed its 14-month investigation delivered “what is intended to be the final knife-thrust in a protracted political assassination”.

His staunch ally, the former culture secretary Nadine Dorries, claimed the report had “over-reached” and that any Tory MP who voted to support it should be deselected.

It means Rishi Sunak faces another bout of bitter Tory infighting in the coming days.

Tory MPs will not be whipped when the report is debated on Monday, Mr Johnson’s 59th birthday, allowing some to avoid taking a side by abstaining or being absent.

The former Tory leader was found to have repeatedly and deliberately misled MPs over the Partygate affair, when Covid lockdown rules were breached in Downing Street.

READ MORE: Boris Johnson guilty of deliberately and repeatedly misleading MPs

The report by the Privileges Committee said he had “closed his mind to the truth” and committed contempts of parliament by not being honest over his knowledge of the affair.

The MPs on the committee also said Mr Johnson had committed a further serious contempt by leaking their provisional findings when he quit as an MP last week.

By claiming to be the victim of a “kangaroo court” and a “witch hunt”, Mr Johnson contributed to a campaign of abuse and “attempted intimidation” against the committee, the MPs said.

It was an unprecedented verdict on a former PM, and a withering judgment on Mr Johnson’s character and conduct which makes a political comeback all but impossible.

The seven-member committee said that if Mr Johnson was still an MP he should be suspended for 90 days. 

It recommended he be denied the Commons pass routinely given to former MPs.

The Commons is due to debate the 108-page report on Monday.

Despite the forensic criticism of his actions, Mr Johnson, who received a police fine for breaking lockdown rules in No10 despite denying wrongdoing, tried to dismiss the findings.

He said: "The committee now says that I deliberately misled the House, and at the moment I spoke I was consciously concealing from the House my knowledge of illicit events.

“This is rubbish. It is a lie. In order to reach this deranged conclusion, the committee is obliged to say a series of things that are patently absurd, or contradicted by the facts."

The Covid-19 Bereaved Families for Justice UK group said the report was "another grim reminder" of how the former PM broke his own rules "so he could have a party and a laugh" as families said "goodbye to loved ones over Zoom".

Spokesman David Garfinkel said: "Johnson has shown no remorse.

"Instead he lied to our faces when he told us that he’d done 'all he could' to protect our loved ones. He lied again when he said the rules hadn’t been broken in number 10, and he’s lied ever since when he’s denied it again and again.

"It’s an utter tragedy that Johnson was in charge when the pandemic struck and he should never be allowed to stand for any form of public office again."

Deputy Labour leader Angela Rayner said Mr Johnson's response showed he was a "pound-shop Trump".

She said he had shown contempt for the parliamentary process and let down those who put "so much trust, faith and confidence" in him.

She said: "Boris Johnson is not only a law breaker but he's a liar."

Asked about his claim to be the victim of a plot to ruin him, she said: "I think it's a load of rubbish, and he knows it... That's why he's resigned.

"He needs to apologise for what he's put the public through - he won't though because Boris Johnson never accepts responsibility for what he does."

The Liberal Democrats called for Mr Johnson to be stripped of the £115,000 annual allowance available to former prime ministers to run their office.

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Edinburgh West MP Christine Jardine said: “People across Scotland and the UK are sick of the sleaze, chaos and law-breaking that has come to define the Conservative party.

“This report should be the final nail in the coffin for Boris Johnson’s political career and the Scottish Conservatives who endorsed and defended him.

“Rishi Sunak must cut off Johnson’s ex-Prime Minister allowance to stop him milking the public purse for his own personal gain. Anything less would be an insult to bereaved families who suffered while Boris Johnson lied and partied.”

SNP Westminster leader Stephen Flynn said: "For people in Scotland the message is clear - independence is the only way to escape Westminster control and get rid of unelected and unaccountable Tory governments for good.

"The damning report into Boris Johnson shows he repeatedly lied to the public and parliament. Rishi Sunak must respond with tough action against his disgraced Tory predecessor - removing his taxpayer-funded allowance, binning his honours list, and recouping his legal fees.

"Johnson may be gone from parliament but his toxic legacy lives on - with the Tories and pro-Brexit Labour Party both imposing Brexit and austerity cuts, attacking devolution, and denying Scotland's democratic right to choose our own future.

"The SNP is the only party offering real change with independence - and independence is the only way to stop Scotland being ruled over by Tory governments we don't elect."