Tony Blair is likely to stand down early if charges are brought in the cash-for-honors affair against any of his key aides, including Ruth Turner, arrested on Friday on suspicion of perverting the course of justice.
Ministers said they were certain Blair would not seek to stay until his planned departure date of June or July if any of his immediate entourage were charged.
One senior Labor minister said: "He knows he would need to do the right thing for the party."
The cash-for-honors inquiry was launched in March last year after complaints from two MPs that wealthy individuals who lent millions of pounds to Labor were later nominated for peerages, and was later extended to cover the Conservatives.
Senior ministers said Blair remained convinced of Turner's innocence and remain doubtful that the police have as reported at the weekend hacked into No 10 computers to show that she and other Downing Street aides have not been cooperating with the inquiry team.
But while any decision to lay charges would not necessarily lead to convictions, it would represent a dramatic raising of the stakes, and undermine Downing Street's suggestions that the investigation is based on a bogus interpretation of the law. The minister added that if anyone were charged it might become impossible to govern. "The focus would drift away from what he is trying to do."
The Guardian has previously reported that the police had commissioned advice from computer experts in an effort to find deleted e-mails or computer records.
In an attempt to ease the tension between No 10 and the police over the manner of Turner's arrest, the lord chancellor, Lord Falconer, said it would be best if the government remained silent.
But officials were still arguing, privately and publicly, that the Met had acted in an unnecessary way by arriving at Turner's front door at 6.30 am with four officers determined to search her home.
Turner's friends said she and her lawyers have cooperated fully with the inquiry. If no charges are brought at the end of this year-long investigation, some senior Labor figures intend to voice their views on the police behavior in the strongest terms.
The culture secretary, Tessa Jowell, said at the weekend she was "slightly bewildered" by the Met's behavior and the former Home Secretary David Blunkett again questioned the police's tactics on Sunday, saying Turner had been treated in the manner of a drug dealer.
(China Daily January 23, 2007)