The head of the Commons ‘sleaze’ watchdog has warned tactics used by No 10 to get Tories seeking to oust the Prime Minister to back down are illegal.

Commons Standards Committee chairman Chris Bryant said threats to withdraw funding from MPs’ constituencies amounted to ‘misconduct in public office’.

He said there were even allegations the Prime Minister had been directly involved as he battles to save his job in the fallout of partygate.

No 10 is braced for an eagerly awaited report next week by Sue Gray, the senior civil servant investigating lockdown parties in Downing Street and elsewhere in Whitehall.

It is likely to fuel from opposition parties for a police investigation if there is any evidence Covid rules were broken – including at a drinks do in May 2020 attended by Mr Johnson.

Mr Bryant, a Labour MP, said he had spoken to ‘about a dozen’ Conservatives in recent days.

Boris Johnson is fighting for political survival as he continues to be dogged by partygate

They claim to have either been threatened with having pubic funding cut from their constituencies or promised more funding if they voted ‘the right way’, the chairman revealed.

‘I have even heard MPs alleging that the Prime Minister himself has been doing this,’ Mr Bryant told the BBC Radio 4 Today programme.

‘What I have said to all of those people is that I think that is misconduct in public office. The people who should be dealing with such allegations are the police.

‘We are not the United States. We don’t run a ‘pork barrel’ system. It is illegal. We are meant to operate as MPs without fear or favour.

‘The allocation of taxpayer funding to constituencies should be according to need, not according to the need to keep the Prime Minister in his job.’

Tory backbencher William Wragg says he is meeting a Scotland Yard detective next week over ‘blackmail’ claims

His intervention came after William Wragg, the senior Tory MP who first raised concerns about attempted ‘blackmail’ by No 10, disclosed that he is to meet police to discuss his claims.

Earlier, he said he would be meeting a Scotland Yard detective in the House of Commons next week, raising the prospect police could open an investigation.

The disclosure came after Downing Street said it would not be mounting its own inquiry into the claims, despite calls to do so by both Conservative and opposition MPs.

A No 10 spokesman said it would only open an inquiry if it was presented with evidence to back up Mr Wragg’s assertions.

However, the MP, who chairs the Commons Public Administration and Constitutional Affairs Committee, said he believed an investigation should be for the ‘experts’ in the police.

Johnson was dealt another embarrassing blow when Bury South MP Christian Wakeford defected to Labour

He told The Daily Telegraph that he would outline ‘several’ examples of bullying and intimidation, in some cases involving public money.

Mr Wragg added: ‘I stand by what I have said. No amount of gas-lighting will change that.

‘The offer of Number 10 to investigate is kind but I shall leave it to the experts. I am meeting the police early next week.’

A Metropolitan Police spokesman said: ‘As with any such allegations, should a criminal offence be reported to the Met, it would be considered.’

Mr Wragg, one of seven Tory MPs to have called publicly for the Prime Minister to resign, stunned Westminster with his allegations this week of a campaign of intimidation by No 10.

Christian Wakeford, the Bury South MP who defected to Labour, later described how the Tory whips had warned him over funding for a new school in his constituency if he rebelled in a vote over free school meals.

Ministers have sought to dismiss the allegations, insisting the whips had no role in the allocation of public funding.

The latest disclosures will only fuel the febrile mood at Westminster, with Mr Johnson’s political survival hanging in the balance.

Mr Wakeford’s defection earlier this week appeared to have put the plotting on hold as Tory MPs publicly rallied behind the leadership while the rebels largely went to ground.

However, the publication of Ms Gray’s report represents another moment of danger for Johnson.

It could potentially trigger a fresh wave of letters to the chairman of the Tory backbench 1922 Committee Sir Graham Brady.

Under party rules there will be a confidence vote in Johnson if 54 of the party’s MPs write to Sir Graham calling for one.

The PM is expected to spend the weekend at Chequers, his official country residence, ringing round potential rebels urging them not to plunge the dagger.

The Times reported Mr Johnson had reassembled the ministerial team which helped him mount his successful leadership bid in 2019 as he seeks to shore up support.

Transport Secretary Grant Shapps is reportedly playing a key role in the operation along with three former whips and other loyalists.