John Prescott should have known his visit to the ranch of a man bidding to build Britain's first super-casino was problematic, the parliamentary watchdog has said.
The committee on standards and privileges warns the deputy prime minister should have realised staying at Philip Anschutz's ranch last summer was potentially a conflict of interest under the ministerial code and the regulations on MPs' interests.
Only Tony Blair can rule on breaches of the code, but today's report says this causes confusion, and recommends he consider introducing an independent body to investigate allegations of breaches of the code.
In its investigations into Mr Prescott's behaviour as an MP, the committee says he will face no disciplinary action for failing to declare the visit on the register of MPs' interests, as he had since done this, albeit 11 months late.
But it warned his case was a "cautionary tale", noting that Mr Prescott should have addressed whether his visit was in breach of the code's guidance about hospitality that "might reasonably be thought" to influence his behaviour as a minister.
In a statement, Mr Prescott said he accepted the committee's findings, and Downing Street said the row about Mr Anschutz and the dome, where the American billionaire is hoping to build Britain's first regional casino, was now over.
However, today's report has only fuelled opposition calls for Mr Blair to order a full investigation, with shadow culture secretary Hugo Swire warning: "According to the report, even Mr Prescott now accepts that there was a perceived conflict of interest.
"The prime minister cannot ignore the now overwhelming view that by staying at the ranch and accepting the gifts, Mr Prescott breached the code.
"It is simply untenable for Mr Blair not to launch an immediate investigation into the clear conflict of interest that has arisen. If he fails to do so, then any remaining shred of integrity that his government has will be in tatters."
Last night, parliamentary sleaze watchdog Alistair Graham also urged the prime minister to launch an investigation, warning that whatever the outcome of today's report, it did not solve the most serious issue of whether Mr Prescott broke the ministerial code.
Today's report does not look at whether the gifts Mr Prescott reportedly received during his stay last summer should have been declared on the register of interests, as they were received in his ministerial capacity.
But the committee expresses concern about how such ministerial gifts are reported, and welcomed Mr Prescott's decision to conduct an urgent review of his department's procedures.
It also calls for a "transparent, standardised and timely procedure" for the reporting of all ministerial gifts, saying John Bourn, who was appointed the independent advisor on the ministerial code earlier this year, should look into it urgently.
To read the report on John Prescott, click on the committee on standards and privileges website