Gordon Brown is coming under pressure over MPs' expenses, after the man tasked with cleaning up Westminster said he was "disappointed" that the Queen's Speech contained no legislation to implement his recommendations.
Downing Street insisted the Prime Minister was not seeking to block Sir Christopher Kelly's reforms, but the chairman of the Committee on Standards in Public Life said that a bill was needed to ensure 11 measures are in place before the general election.
In an apparent concession to Sir Christopher, Number 10 said the PM was ready to bring forward any legislation needed to complete his reforms "on a cross-party basis as required".
But the move drew accusations of a U-turn from Conservatives, who pointed out that Mr Brown had brushed aside an earlier offer from David Cameron of Tory help to rush the measures onto the statute book.
The row blew up amid reports that police may be about to pass files to the Crown Prosecution Service on six MPs and peers caught up in the expenses scandal, with a possible decision on charges in January.
Scotland Yard described as "speculation" a report in the Daily Telegraph that the Director of Public Prosecution Keir Starmer will imminently receive files on Labour MPs Elliot Morley, David Chaytor and Jim Devine, Labour peers Baroness Uddin and Lord Clarke of Hampstead and Tory Lord Hanningfield.
The bulk of the most dramatic measures in this month's Kelly Report - such as banning the employment of MPs' spouses and ending taxpayer funding for mortgages - can be implemented without further legislation.
But Sir Christopher believes that key measures must be passed into law by Parliament, and on Wednesday night said that it was "very important" that this was done before the election to allow the new generation of MPs arriving at Westminster to start with a clean slate.
They include provisions to bolster the independence of the new Independent Parliamentary Standards Authority, to give it responsibility for setting MPs' pay and to beef up its powers to investigate and punish errant MPs, as well as a requirement for parliamentary candidates to register their interests and a ban on MPs serving in devolved assemblies.
Downing Street insisted it was not "standing in the way of any of Kelly's recommendations".