In a withering assault on the previous Tory chief, who stood down as Uxbridge and South Ruislip MP on Friday night time, his predecessor mentioned Mr Johnson’s time in workplace amounted to an assault on “one of the bedrocks of democracy”.

In his letter of resignation, Mr Johnson mentioned the Commons investigation into whether or not he misled Parliament over lockdown events was an try and “drive me out”.

During an look on the Kite Festival in Oxfordshire, Sir John, 80, mentioned: “When Boris attacked the committee that, he tells us, was about to report that he misled – that is lied – to the House of Commons on a number of occasions about the lockdown parties.

“When he accuses them...not only does he insult a parliamentary committee, but suggest they are his worst enemy, whichis not true.

“My perception is that the worst enemy for Boris Johnson is in fact Boris Johnson.”

READ MORE: Zahawi 'on point' of quitting with Sharma '50/50' and two others 'ready' to go

Sir John, who was prime minister from 1990 till 1997, mentioned Mr Johnson, 58, was damaging democracy along with his actions.

He mentioned: “To attack the institution of Parliament is to attack one of the bedrocks of democracy.

“Another thing, the Government, just like the average citizen, is absolutely compelled to obey the law.”

Sir John added: “You can swiftly undermine the conventions that hold Parliament together, but it is not just that, there are conventions of behaviour.

“And what has happened during Boris Johnson’s government is that they have ransacked this, ignored them and that is immensely damaging.”