It comes as the caretaker prime minister is said to be consulting with lawyers on the best way to handle the Commons privileges committee probe set to begin in the autumn.
Johnson ally Nadine Dorries has been accused of waging a “terrorist campaign” to discredit the inquiry, after she urged Tory MPs on the cross-party committee to quit the “witch hunt”.
In an email to all Tory MPs, chief whip Chris Heaton-Harris said he wanted to “remind” them that MPs had already voted to set up the inquiry – and would get to vote on any punishment recommended by the committee.
“May I urge caution against any further comments in the media about the privileges committee and especially its clerk and members,” he also warned over increasingly bad-tempered rows over the probe.
Heaton-Harris added: “Invariably these comments will be misinterpreted by those who do not wish to help us.”
Senior Conservative MP Sir Bernard Jenkin – who sits on the committee set to probe the PM – lashed out when asked about Dorries claims of a “witch hunt”.
“If people wish to criticise it please write to the committee – don’t just conduct a sort of terrorist campaign to try and discredit the committee,” he said when asked about the culture secretary’s attacks.
Meanwhile, Johnson is consulting lawyers over the best way to approach the privileges committee inquiry, according to The Times.
Allies also told the newspaper that they accept it now a “foregone conclusion” that he would be found in contempt of parliament.
But the PM hopes to avoid a 10-day suspension from the Commons – a sanction that would allow his Uxbridge constituents to start a recall petition and possible by-election – if he has not found to have “knowingly” misled parliament.
Mr Johnson denies misleading parliament over what he knew of rule-breaking gatherings inside Downing Street.
His defenders have questioned whether he “deliberately” or “knowingly” misled parliament during the Partygate saga. But the committee made clear that such commentary is not relevant to whether he was in contempt.
A memo states: “It is for the committee and the House to determine whether a contempt has occurred and the intention of the contemnor is not relevant to making that decision.”
Three former officials at No 10 reportedly believe that the PM did not tell the Commons all that he knew about rule-breaking gatherings held during the Covid crisis.
One of the ex-staffers has agreed to give evidence to the privileges committee inquiry into whether the PM misled parliament, while two others contacted by the committee are considering whether to testify, according to The Telegraph.