Tony Blair must investigate whether John Prescott has breached the ministerial code to avoid appearing "lax" about standards, parliament's sleaze watchdog has warned.
Alistair Graham said the prime minister would "clear the air" by ordering a probe into his deputy's meetings with American billionaire Philip Anschutz, whose firm is bidding to host Britain's first super-casino at the dome.
His call yesterday came after the Mail on Sunday reported that Mr Prescott was presented with a Stetson hat, tooled leather boots and a belt with his initials, 'JP', on the silver buckle during his stay at Mr Anschutz's Colorado ranch last July.
The deputy prime minister is already being investigated for failing to declare this weekend visit in the register of MPs' interests until last week, and questions are now being asked whether he also failed to declare these gifts.
Philip Mawer's investigation is concentrating on Mr Prescott's role as an MP, but the Conservatives and Liberal Democrats are both pressing for an inquiry into whether his meetings with Mr Anschutz also breached the ministerial code of conduct.
This states that "no minister or public servant should accept gifts, hospitality or services from anyone which would, or might appear to, place him or her under an obligation".
The Hull East MP has denied having anything to do with the government's casino policy, and insisted all his meetings with Mr Anschutz were about the regeneration of east London, in which the work on the dome was a large part.
Mr Blair is the only person who can launch an investigation into possible breaches of the ministerial code, although he appointed the head of the National Audit Office (NAO), John Bourn, as special advisor to ministers on the issue earlier this year.
Speaking to BBC Radio Four's The World This Weekend yesterday, Sir Alistair said it was in the prime minister's interest to begin a probe, to prove his determination to uphold the highest standards of ministerial behaviour.
"It does seem when these issues relate to a central aspect of government policy in terms of casinos, the future of the dome, planning issues like that, it would be much better to clear the air by invoking the procedure to ask John Bourn to carry out an investigation," the chairman of the committee on standards in public life said.
"I think the prime minister and the government would be better positioned in dealing with these issues if they used the procedure that he himself introduced only fairly recently.
"Otherwise you lay yourselves open to the criticism either that you are rather lax or don't care sufficiently about standards issues, or political considerations in terms of whether there could be a deputy leader election - all those sorts of political-type issues - are uppermost in your mind rather than what is proper from a public point of view."
Meanwhile, health secretary Patricia Hewitt told BBC One's Sunday AM that much of the media stories about Mr Prescott were "speculation and froth", and rejected claims that environment secretary David Miliband was being lined up to take his job.
"There is no vacancy at the moment for deputy leader or deputy prime ministers and John Prescott, like all the rest of us in government, are just getting on with what we were elected to do," she said.