The findings follow an investigation by Kathryn Stone, the Parliamentary Standards Commissioner, which began in May 2020 following a rule change that allowed the authorities to investigate historic allegations of bullying.

It concluded that Mr Bercow displayed “intimidatory and undermining” behaviour and “threatening conduct”, including “verbal abuse and displays of anger”.

It also found that he bullied Lord Lisvane, a former Clerk of the Commons, who was subjected to “a sustained course of conduct” involving “unfounded criticism” that was “often made at length and at volume and included derogatory inferences about [his] upbringing and background”.

Allegations were also made against Mr Bercow by Angus Sinclair, a former member of Commons staff, and Kate Emms, who still works in Parliament.

The findings were assessed by the Independent Expert Panel (IEP), which heard appeals from Mr Bercow but upheld the 21 findings against him.

“The findings of the Parliamentary Commissioner for Standards, which we have upheld, show that the respondent has been a serial bully,” the IEP said. “His evidence in the investigations, the findings of the commissioner and his submissions to us show also that the respondent has been a serial liar.

“His behaviour fell very far below that which the public has a right to expect from any Member of Parliament.”

‘Findings of a kangaroo court’

Responding to the report, Mr Bercow said he had been subject to the findings of a “kangaroo court”, questioned the process of the investigation and insisted he had enjoyed good relations with staff.

“All I can say is that the case against me would have been thrown out by any court in the land since it is based on the flimsiest of evidence, rooted in hearsay and baseless rumour, and advanced by old school dogmatists once intent on resisting change at all costs and now settling some ancient scores with me,” he said.

“Add to that a dash of personal spite and you have some idea of the vengeful vendetta mounted against me. It is a travesty of justice and brings shame on the House of Commons.

“This has been a protracted, amateurish and unjust process which would not have survived five minutes’ scrutiny in court. To describe what I have experienced as a kangaroo court is grossly insulting to kangaroos.

“None of the investigators is a lawyer, and the commissioner overseeing them has no expertise whatsoever in the consideration of alleged bullying.

“Throughout, gossip from absent friends of the complainants has been treated as the absolute truth, whilst eyewitnesses who challenged the allegations were described as ‘not helpful’ and discounted. The commissioner even presumed to make findings on matters about which I was never questioned.”

He added that the idea he had been banned from Parliament for life was “establishment spin” and pointed out that he could still attend debates as a guest of someone else.