As a Commons committee delays an investigation into political honours, the Conservatives have again been urged to reveal the names of those who have loaned them money.

MPs on the public administration committee confirmed on Monday night that they would delay a planned session with Chai Patel and Sir David Garrard, who have lent Labour more than £3m.

The decision was taken after the police warned the hearings could compromise any future trial that might result from an investigation into whether honours had been sold.

The Metropolitan Police is conducting an inquiry into allegations that offences had been committed under the 1925 Honours (Prevention of Abuses) Act.

And in a letter to the committee, deputy assistant commissioner John Yates said the investigation could become a corruption inquiry.

"Whilst it may be too early for us to widen our investigation into the arena of corruption, I certainly have not ruled this out," he wrote.

"My concerns were that your scrutiny could be viewed as an abuse of process in terms of fairness in any future potential criminal trial.

"I have consulted closely with senior lawyers from the Crown Prosecution Service about this matter. They share my concerns and are happy for them to be articulated in this letter."

Delay

Confirming it would delay the hearings following the police request, the committee said: "The matters alleged go to the heart of the political and parliamentary process, and we think it vital that parliament should investigate as soon as possible."

"In the light of advice, we have decided to have a short pause in our inquiry, of no more than a matter of weeks, to allow the police to tell us whether there is a realistic prospect of charges being brought," the MPs added.

"We wish to make it clear that we will resume our investigation as soon as possible. We will reschedule our hearings,and we expect all witnesses to cooperate.

"We will not hesitate to use our powers to compel attendance, if necessary."

Number 10 on Tuesday said the police had not been in touch in relation to the investigation.

Loans

Meanwhile, pressure has grown for the Conservatives to name the people who have lent the party money.

Former party treasurer Lord McAlpine said the financial supporters should be told that "it's greatly to our disadvantage to preserve this anonymity, please can we release your names?".

"If the loans are completely honest and straightforward, there should be no reason why anyone should worry about that," he told the BBC Radio 4 Today programme.

And former chancellor Kenneth Clarke told BBC 2's Newsnight: "I think that all loans should be declared but I gather that problem is that confidentiality agreements were entered into."

He added that the row was doing "huge damage to all political parties and to the political system".

"I am very suspicious of all these loans. I think most of them were drafted as loans, because they were actually donations, to get round the legal provisions that require them to be disclosed if they were just donations," Clarke added.

"The parties presumably didn't intend to pay back any of these loans because political parties cannot generate revenue to pay back loans of this kind usually.

"I think that the whole thing is a very, very serious constitutional scandal."