A TOP QC is set to suggest the partygate probe into whether Boris Johson misled parliament could endanger democracy, insiders have claimed. 

Lord Pannick, who acted against the UK Government in landmark Brexit cases including representing Gina Miller in 2016, is expected to argue that the way the inquiry is being dealt with might effectively gag ministers and inject fear into them about saying the wrong thing, according to a senior source.

It is feared many may in future try to avoid giving detailed answers and promise MPs facts and figures at a later date. 

The Commons privileges committee has threatened to punish Johnson if he is found to have misled the House, whether on purpose or not.

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The senior source, who has seen the legal intervention due to be published by Downing Street on Friday, told the Daily Mail: "This isn’t for Boris, but for all future PMs and MPs.

"Ministers will never be able to say anything if they think they can be found in contempt by accidentally giving the wrong answer."

Lord Pannick's legal opinion is thought to have been commissioned over fears about how the investigation could affect the functioning of government. It is expected to focus on an unexpected change to the terms of reference of the inquiry.

Ministers are usually punished only if they are found to have knowingly misled MPs, but the committee decided in July not to take the Prime Minister’s intentions into account when he told the House last year that "the rules were followed at all times".

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If Johnson is found guilty of contempt he could be suspended from Parliament and face losing his seat.

The committee said it would follow the interpretation of the Clerk of the Journals, Eve Samson, who said: "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."

Supporters of the PM argued Lord Pannick's advice should mean the end of the probe.

Culture Secretary Nadine Dorries said: "This expert legal opinion shows the inquiry was a biased, Kafkaesque witch-hunt. It should now be halted."

An insider of the QC's advice said: "It is absolutely devastating."

The advice was commissioned by the Office of the Prime Minister, which sits within the Cabinet Office. 

Tory Leadership frontrunner Liz Truss has said she would vote against the inquiry which comes after a criminal investigation by Scotland yard that led to Johnson receiving a fine.

However, her rival Rishi Sunak has said it should be allowed to continue.