The former Conservative MP Christian Wakeford has alleged that party whips told him he would lose funding for a new high school in his constituency if he did not vote with the government.

The claim came as the senior Conservative William Wragg urged MPs to report government ministers, whips and advisers to the Speaker – and even the police – for what he claimed was attempted blackmail of some colleagues suspected of possibly opposing Boris Johnson.

Anger among Johnson critics escalated again on Thursday after sources briefed that rebels were losing their nerve. Another MP opposing Johnson denied that letters of no confidence had been withdrawn after Wakeford defected to Labour.

“These briefings of withdrawals are pure invention from No 10,” one said. “Wakeford may have stayed some people’s hands yesterday but this isn’t going into reverse.”

Speaking at a Labour event on Thursday, Wakeford backed up the claims by Wragg that threats involving public money were made by the whips.

“I was threatened that I would not get a school for Radcliffe if I did not vote in one particular way,” he said. “This is a town that has not had a high school for the best part of 10 years.

“How would you feel when they hold back the regeneration of a town for a vote. It didn’t sit comfortably. That was the start of me questioning my place, where I was and ultimately to where I am now.”

Wragg, who chairs the public administration and constitutional affairs committee (PACAC), which looks into the work of government and the civil service, said whips had threatened to withdraw funding from the constituencies of MPs opposing Johnson.

Speaking at the start of a hearing of the PACAC, attended by Steve Barclay, the Cabinet Office minister, and Alex Chisholm, the department’s most senior civil servant, Wragg said he believed the actions breached the ministerial code.

“In recent days a number of members of parliament have faced pressures and intimidation from members of the government because of their declared or assumed desire for a vote of confidence in the party leadership of the prime minister,” he said.

“It is, of course, the duty of the government whips’ office to secure the government’s business in the House of Commons. However, it is not their function to breach the ministerial code in threatening to withdraw investment from members of parliaments’ constituencies which are funded from the public purse.

“Additionally, reports to me and others of members of staff at No 10 Downing Street, special advisers, government ministers and others encouraging the publication of stories in the press seeking to embarrass those who they suspect of lacking confidence in the prime minister are similarly unacceptable.”

“The intimidation of a member of parliament is a serious matter,” he added. “Moreover, the reports of which I’m aware would seem to constitute blackmail.

As such it would be my general advice to colleagues to report these matters to the Speaker of the House of Commons and the commissioner of the Metropolitan police. And they are also welcome to contact me at any time.”

Wragg asked Barclay and Chisholm to convey his concerns to ministers and the civil service, which they said they would.

Johnson said he had seen no evidence to support the claim made by Wragg.

A No 10 spokesperson said: “We are not aware of any evidence to support what are clearly serious allegations. If there is any evidence to support these claims we would look at it very carefully.”

The Speaker, Lindsay Hoyle, said allegations about potentially criminal offences would be a matter for the police. “While the whipping system is long established, it is of course a contempt to obstruct members in the discharge of their duty or to attempt to intimidate a member in their parliamentary conduct by threats,” he said.

Angela Rayner, Labour’s deputy leader, said the alleged threats to withdraw investment to force support for Johnson were “disgusting”. She said: “These are grave and shocking accusations of bullying, blackmail, and misuse of public money and must be investigated thoroughly.”

Ed Davey, the Liberal Democrat leader, said the claims showed Downing Street was “now in full scorched earth mode”. He said: “All Boris Johnson cares about is saving his own skin. He’s acting more like a mafia boss than a prime minister.”

Wragg was one of the first Conservative MPs to call publicly for Johnson to go because of allegations about lockdown-breaching Downing Street parties, saying the prime minister’s position had become untenable.

For Johnson to face a confidence vote among his MPs, 54 of them – 15% of the total – would need to submit letters seeking this to the 1922 Committee, which represents backbenchers. There have been regular predictions this week that the total was about to be met, but it has not yet happened.

Wakeford, introducing a speech by Rachel Reeves in Bury the day after his defection, said it was “a great honour, if not a surprise, to be here today”.

He said Labour was “ready to provide an alternative government that this country can be proud of. and deserves, and certainly not to be embarrassed by, that is one of the reasons I am here today.”.