Orris Johnson will submit a written dossier of evidence to MPs as he tries to clear his name over allegations he misled Parliament over the Partygate scandal.
As the former prime minister fights to save his political career, his friends will make it a “bombshell” dossier to the Privileges Committee.
Mr Johnson will appear for a televised grilling before the panel on Wednesday, and it is expected he will submit his written evidence before then.
In an interim report, the Privileges Committee said the evidence strongly suggested that the breach of coronavirus rules at No 10 should have been “obvious” to Mr Johnson.
They are examining evidence surrounding at least four occasions when he may have deliberately misled MPs by assuring the Commons that the rules had been followed.
Mr Johnson’s aides said he would provide a “comprehensive and compelling” account to the committee ahead of his appearance, showing he had not “deliberately misled the House”.
The Sunday Times reported that he will point to a series of previously anonymous WhatsApp messages from senior civil servants and members of his No.10 team that show he relied on their advice when giving his statements to Parliament.
He will also publish messages which show other senior Downing Street figures believed the gatherings were covered by a “workplace exemption” to the lockdown rules.
The committee’s inquiry is being chaired by Labour’s Harriet Harman, although the seven-strong panel has a Tory majority.
The committee will publish its findings that Mr Johnson is in contempt of Parliament and recommend any punishment, but the final decision will rest with the full House of Commons.
Prime Minister Rishi Sunak has said he will not try to influence MPs on the committee and has indicated he will give Conservative MPs an independent vote on any approval he may recommend.
Asked if he was concerned that a suspension of more than 10 days could lead to a by-election in Mr Johnson’s Uxbridge and South Ruislip seat, Mr Sunak added: “It’s a matter for Parliament, for the House. It is not appropriate to involve the government in this.”
