British work and pensions secretary Peter Hain is facing the prospect of a parliamentary inquiry as he struggles to save his Cabinet career.
The Parliamentary Commissioner for Standards, John Lyon, is considering a formal complaint that Mr Hain broke Commons rules by failing to declare more than £100,000 in donations to his Labour deputy leadership campaign.
If the complaint is upheld, Mr Hain could face sanctions ranging from a rebuke by the powerful Commons Standards and Privileges Committee to suspension from the House - which would almost certainly spell the end of his ministerial career.
Mr Hain has already admitted in a statement yesterday that he failed to declare 17 donations totalling £103,156.75 to the Electoral Commission - the official elections watchdog.
However Tory MP David Davies, who lodged the latest complaint, said that Mr Hain had also breached House of Commons rules by failing to declare them in the Register of Members' Interests.
"Clearly, based on what Peter Hain has said, there has been a breach of the rules," he said.
Downing Street said that Mr Hain still had Gordon Brown's support. "The Prime Minister has full confidence in Peter Hain," a No 10 spokeswoman said.
However opposition MPs warned that his position, which he combines with the job of Welsh Secretary, was becoming increasingly untenable.
Mr Davies said that the Register of Members' Interests was part of the "constant background of the lives" of all MPs and he could not understand how Mr Hain could overlook such a large sum of money.
"I really find it hard to see how he can continue in both these important positions if he is the sort of man who forgets about £100,000," he said. "I think there are a lot of questions to be answered. It does raise questions about his continued career."
Plaid Cymru's Westminster leader Elfyn Llwyd, said: "The whole thing, I think, is a total circumvention of all the rules appertaining to elections and I think that, as a Cabinet minister, it will be very difficult for him to stay in office."
Mr Lyon, who only took up his post on January 1st, will now have to decide whether the complaint warrants a full-blown inquiry.
PA