Lord Neill, chair of the Committee on Standards in Public Life, said the prime minister should make clear his commitment to the government's ministerial code of conduct in the light of the Hinduja passports affair.

He said the code should be rewritten to include a declaration by the prime minister that he is personally responsible for minister's conduct.

Lord Neill said the code should set out what punishment would be meted out to transgressors.

Opposition MPs have accused Europe Minister Keith Vaz of not coming clean about his involvement in the passport application affair that forced Peter Mandelson from office.

Mr Vaz has admitted making representations to the government on behalf of the controversial Indian billionaires, the Hinduja brothers, in 1997, but says he did nothing wrong.

There are MPs who have got legitimate questions to ask and are getting stonewalled

Lib Dem MP Norman Baker

He says he is "very happy" to have his correspondence on the affair published, but not until the findings of a government inquiry into the incident are made public sometime in the weeks ahead.

But Lord Neill said recent events suggested there was a need for Mr Blair to make a clear commitment to the ministerial code of conduct.

He told BBC Radio 4's Today programme on Saturday: "The code does need a very clear statement from the prime minister that he is to be the judge of the requirements of the code and what the consequences are for breach of it."

He said while he did not expect Mr Blair to become involved in "trivial" allegations, he was responsible for adjudicating on major complaints relating to his ministers.

Seeking answers

Opposition MPs have accused Mr Vaz of hiding behind the inquiry, headed by Sir Anthony Hammond.

Shadow Home Secretary Ann Widdecombe said questions needed to be answered.

She has tabled a series of questions in the Commons about the alleged involvement of various ministers in the applications.

"The big issue in all of this must be was there a direct connection between the �1m the Hinduja brothers promised for the Dome and the speeding up, or indeed possibly the success, of their passport applications," she said.

Liberal Democrat MP Norman Baker said he was also seeking more answers.

'Stonewalled'

He said: "We need to know exactly who lobbied whom and when, and for what purpose.

"The whole thing cannot be suspended without any further inquiry from anybody until such time as Sir Anthony Hammond is ready.

"There are MPs who have got legitimate questions to ask and are getting stonewalled by answers from the home secretary and others.

"That is not helpful to the government."

Mr Mandelson resigned from the Cabinet on Wednesday, after admitting he had made misleading statements over the passport application.

'Foolish'

Despite his resignation, his Hartlepool constituency confirmed on Friday night that he will stand as their candidate in the next general election.

Sir Anthony Hammond has already begun work on his report and Downing Street has said he will complete it "as quickly as possible, consistent with a proper and thorough investigation".

A spokesman for the prime minister denied claims the government was using the inquiry to dodge questions.

"There's no question of hiding behind anything," he said

Meanwhile, the prime minister said of Mr Vaz: "From the look of the papers I have seen I cannot see anything wrong with what has been done.

Srichand Hinduja: Passport application led to Mandelson's downfall

"Keith is a prominent Asian MP, they are prominent people from the Asian community - he made representations on their behalf."

Mr Vaz has defended his actions.

He said the inquiry into the saga would prove that he had done nothing wrong and insisted he would not brief journalists ahead of it.

"I don't want to mislead you," he told reporters.

"There is an inquiry I am not saying anything until I am asked by the chairman [of the inquiry]."

But he added: "Some of you are going to look very foolish when this report comes out.

"Some of the stuff you said about Peter and about others and me you'll regret very much when the facts come out."