David Cameron’s chief Whip Sir George Young faces allegations of using confidential details of Tory MPs’ expenses to “bully” them, and in order to stop them from speaking out against government plans to legalise equal marriage.

Sir George faced allegations from some Tory members who said he had used confidential details of their travel and housing expenses, to “victimise” them.

The Information Commissioner, the Government’s official watchdog, has been consulted by one of the MPs, who has lodged a formal complaint against the Independent Parliamentary Standards Authority (IPSA) for breaking Data Protection and passing information to Sir George.

Speaking to the Mail on Sunday, the anonymous MP said: “Sir George warned me that I should play ball with IPSA, or risk personal financial details being made public. I feel that amounted to blackmail.

“I wrote to Sir Ian Kennedy, the chairman of IPSA, to complain, and received a letter back which told me that, ‘MPs should not be surprised that IPSA has dealings with Chief Whips’.”

“That is why I have complained to the Commissioner. Ipsa should not be passing information to third parties.”

The relationship between IPSA and MPs became fraught with the introduction of a rule which meant they had to hand back a share of the profit made on second homes, meaning some MPs owed more than £50,000.

Sir George has been accused of finding out which MPs owed money to IPSA, in order to “intimidate” them, and to make them back down on issues such as opposition to equal marriage.

A second MP said that he was told by Sir George to settle an expenses claim which had been disputed “if he wanted to be an MP at the next election”.

A third said: “Sir George is trying to find a new way to victimise and bully the rebels, threatening to take their whip away or “tell the boss” if they don’t cough up to IPSA.”

According to the Mail, however, a source close to Sir George denied the allegations, saying: “It is complete paranoid nonsense to suggest that the Chief Whip has in any way used MPs’ expenses difficulties as a way of enforcing discipline. It’s just not his style.

“It is perfectly normal for the Chief Whip to discuss an MP’s expenses with them if there is an issue.

“The information about the expenses of the MP who has complained was  not confidential.”

A spokesman for IPSA said it was “perfectly reasonable” for it to “raise concerns” about MPs to chief whips such as Sir George.

“Where MPs claimed for a subsidy from the taxpayer for their mortgage, we ask for the taxpayer’s share of any increase in the value of the property,’ he said.

“If an MP refused to comply with  that rule, we would challenge that,  and it is reasonable that we raise  our concerns.”

Last weekend Lord Carey accused David Cameron of making Christians feel persecuted through his push for marriage equality.

Members of the Church of England, other faith groups and secularists quickly responded to the claim with strong denials.