Ex-prime minister due at televised Commons committee hearing, with legal team about to publish new evidence backing his claims

A defiant Boris Johnson is preparing an extraordinary televised defence of his actions during the Partygate scandal, as his allies this weekend accused the parliamentary inquiry into the affair of relying on weak evidence compiled by a former civil servant recruited by the Labour party.

With a potentially explosive appearance at the Commons privileges committee due on Wednesday, the Observer can reveal that the former PM’s legal team intends to publish written evidence, including new witness statements, supporting Johnson’s claim that he did not knowingly mislead MPs over lockdown parties – as well as examples of the advice he was given at the time.