Boris Johnson is to submit a dossier of evidence ahead of an interrogation by MPs over whether he lied to Parliament about the partygate scandal.
The former prime minister will provide information in his defence as he prepares for a lengthy televised grilling by the Commons privileges committee on Wednesday, where he faces a fight for his political life.
They are examining evidence around at least four occasions when he may have deliberately misled MPs with his assurances that lockdown regulations were followed.
Mr Johnson, who was fined by the Metropolitan Police for breaching his own COVID-19 laws, has denied deceiving the Commons.
Allies of the ex-Tory leader said he would provide a “detailed and compelling” account to the committee before his appearance, showing that he “did not knowingly mislead the House”.
The Sunday Times reported he will point to a series of previously undisclosed WhatsApp messages from senior civil servants and members of his No 10 team showing that he had relied upon their advice when he made his statements to Parliament.
He will also publish messages which show that other senior figures in Downing Street believed the gatherings were covered by the “workplace exemption” in the lockdown rules.
A committee spokesperson said: “The committee has invited Mr Johnson to provide written evidence to the inquiry, should he wish, in advance of the oral evidence session.
“Any such response will be published.
“The committee has said that Mr Johnson may publish his own written evidence, if he chooses, but any such evidence must also be formally submitted to the committee which will itself publish it as soon as is practicably possible after receiving it, after initial analysis (to make sure no redactions of witness names needed, etc).
“The committee would publish on the website in the usual way.”
The panel’s investigation is being chaired by Labour’s Harriet Harman, although the cross-party group has a Tory majority.
The seven-strong committee will decide whether Mr Johnson committed a contempt of Parliament and recommend any punishment, although the final say would fall to the full House of Commons.
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Cabinet minister Oliver Dowden told Sky News Sophy Ridge On Sunday programme: “I’m sure Boris Johnson will give a robust defence of himself and then it will be for the committee to to determine the outcome of it.”
Prime Minister Rishi Sunak has said he would not seek to influence MPs on the committee and indicated he would grant a free vote to the Conservative ranks on any sanction that may be proposed.
Asked if he was concerned a suspension of more than 10 days could trigger a by-election in Mr Johnson’s Uxbridge and South Ruislip seat, Mr Sunak added: “This is a matter for Parliament, for the House. It’s not right for the government to get involved.”
In recent days, Commons leader Penny Mordaunt warned against intimidation of members on the privileges committee.
She said they must be “permitted to get on with their work without fear or favour” and emphasised they were are “doing this House a service”.
Mr Johnson and his supporters have raised concerns over partygate investigator Sue Gray’s pending move to Labour leader Sir Keir Starmer’s office from the civil service.
However, the committee has denied its inquiry is based on the Gray report.
Instead, the inquiry has taken evidence from witnesses’ WhatsApp messages, emails and pictures from a Downing Street photographer.