Ministers are to be subjected to a new code of conduct to stop them from acting as judge and jury on their own alleged misdemeanours.
The code, to be published in the next few months, will follow recommendations by the Government's standards watchdog, Lord Neill of Bladen.
Under the existing code, ministers are responsible for their own conduct. In future, the Prime Minister will be held accountable for poor behaviour by ministers.
In effect, that will almost certainly mean that Tony Blair will ask the Cabinet Secretary, Sir Richard Wilson, to investigate possible breaches and report to him on them. When Tories complained last month that the Deputy Prime Minister, John Prescott, might have broken the ministerial code by changing rent regulations while he kept a rent-controlled flat in Clapham, their letter was passed back to his department.
In reply to a letter on the subject from Archie Norman, Mr Prescott's shadow on Transport and Environment, the Cabinet Secretary said he had "no comments to make". He wrote: "It is for individual ministers to judge how best to act in order to uphold the highest standards." Under the last government, Jonathan Aitken, then Chief Secretary to the Treasury, was able to clear himself of accusations that his hotel bill at the Ritz in Paris was paid by an arms dealer by lying to John Major and to Sir Robin Butler, the Cabinet Secretary at the time.
However, Lord Neill stopped short of recommending the appointment of an "ethics commissioner" to police the code and Mr Blair is expected to do the same. Instead, he is likely to strengthen the code to reflect that ultimately he is the judge of his ministers' behaviour.
The change was revealed as Tories pressed the Prime Minister to investigate whether Mr Prescott had breached the code over his Clapham flat, which he rents from the Rail, Maritime and Transport Union.
As Secretary of State for the Environment, Transport and the Regions, Mr Prescott passed the Rents Act (Maximum Fair Rents) Order 1999, which limited rent rises on regulated properties.
He could have been a beneficiary of the attempt at rent control, which was subsequently found to be ultra vires by the courts, they said.
Mr Prescott has had his flat since 1970, when anyone whose property had a rateable value of less than £400 could apply for a controlled rent. It is currently occupied by his son as he has an official residence in Admiralty House in central London.
Although the rent control legislation was abolished in 1989, people who still have properties they moved intobefore that date can keep their old, controlled rents.
The Parliamentary Commissioner for Standards, Elizabeth Filkin, has delivered a separate report to MPs on the Standards and Privileges Committee on whether Mr Prescott should have listed the flat in the Register of Members' Interest.
Yesterday the committee deferred a decision on the matter and called for further information. It is expected to publish its findings in May.