Tony Blair is to be called before a Commons committee to give evidence on the ministers' disciplinary code. If he agrees, the appearance will be the first by a serving Prime Minister in more than 50 years.
The Public Administration Committee has written to Mr Blair inviting him to discuss reform of the Ministerial Code, which allows ministers to act as judge and jury on their own alleged misdemeanours. The Government is believed to be planning changes to the code, in response to recommendations by its standards watchdog, Lord Neill of Bladen.
While the committee cannot demand Mr Blair's presence, ministers normally accept invitations to give evidence and a refusal could lead to a Parliamentary fracas. A Downing Street spokeswoman said that Mr Blair had not yet received the letter but when he did he would consider it.
Last night Tony Wright, the chairman of the committee and the Labour MP for Great Yarmouth, said he hoped Mr Blair would agree to make an appearance. He said: "We are on very strong ground in asking him and it would be difficult for him to say it is not his responsibility because it is uniquely his responsibility."
Under the existing code, ministers are responsible for their own conduct. So when the Conservatives complained recently that the Deputy Prime Minister, John Prescott, might have broken the ministerial code by changing the rent regulations while he kept a rent-controlled flat in Clapham, their letter was passed back to his own department.
In reply to a letter on the subject from Archie Norman, Mr Prescott's shadow on Transport and Environment, the Cabinet Secretary, Sir Richard Wilson, said that he had "no comments to make.
"It is for individual ministers to judge how best to act in order to uphold the highest standards," Sir Richard said.
A decision by the Standards and Privileges Committee on whether Mr Prescott broke the separate registration rules for MPs when he failed to list his Clapham flat as a benefit is expected shortly.
After discussing a report from the Parliamentary Commissioner for Standards, Elizabeth Filkin, on Tuesday the committee felt it needed more time to reach a conclusion.
In a report published in January, Lord Neill's Committee on Standards in Public Life suggested the code should be redrafted to make clear that although ministers must judge their own actions and justify them to Parliament, the Prime Minister is their ultimate judge if they misbehave. 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.
A new code is expected to be published in the next few months. In effect, it will almost certainly mean that Tony Blair will ask Sir Richard to investigate possible breaches and report to him on them.
The Government issued the current Ministerial Code after the 1997 general election, and it revised the wording after recommendations by the Neill Committee's predecessor under Lord Nolan. However, Mr Blair rejected the suggestion that it should place the onus on him to judge his ministers, and instead chose a form of words that said they must "retain the Prime Minister's confidence" to stay in office.