Scotland Yard will seek further gagging orders against anyone who could jeopardise the inquiry into whether Downing Street offered loans for honours.

As the 11-month investigation reaches its climax, police are now so concerned that deliberate leaks of information could undermine the chance of a successful prosecution that government lawyers are on alert to prevent the media from publishing more details.

This follows the dramatic move on Friday night by the Attorney-General to take out an injunction against the BBC over a story that revealed why the cash-for-honours probe had widened into one about alleged perversion of justice.

The Times has established that this was not the first time lawyers were consulted over a possible injuction. Scotland Yard was prepared to seek an injunction if the media discovered Tony Blair had been interviewed by detectives for a second time between January 26, when the interview took place, and February 1, the day after Lord Levy, the Prime Minister’s chief fundraiser, was rearrested. Lawyers have threatened several other newspapers with injunctions to stop them from publishing details of the e-mail.

The e-mail obtained by the BBC is understood to be from Ruth Turner, the director of government communications, to Jonathan Powell concerning Lord Levy, the Prime Minister’s fundraiser.

The e-mail is alleged to be capable of being interpreted as evidence of an attempted cover-up. The Times can also reveal that: The injunction was taken out in order to stop a third party, whose identity has not been revealed, from finding out about the e-mail. It suggests someone who has not yet been arrested may be a focus of the inquiry. The Sun was last night threatened with legal action by the Attorney General’s office if it printed details of the e-mail The Attorney-General has played a personal role all along the proceedings. The Times understands that he was personally involved, by telephone, on Saturday in the decision to threaten a second injunction against the Mail on Sunday.

Downing Street was last night accused by Angus MacNeil, the SNP MP, of leaking the e-mail. But the claim was denied by Downing Street. A source said that they were “very confident” that the leak did not come from Government.

There was confusion last night over what could still be reported. The details of the BBC injunction have not been made public, and the terms are said to be “very restrictive”. However Sunday newspapers went much further without any action by the Attorney-General.

A spokesman for the Attorney-General denied reports that they had attempted to stop the media reporting the injunction. “At no point did we ask for the fact of the injunction to be kept secret. The fact of the injunction is clearly not secret. The terms of the injunction are confidential between the parties by order of the judge, and we cannot comment further.”

Angus MacNeil, the SNP MP who made the initial complaint to police, said: “Downing Street has shot itself in the foot over this. First they get into a problem over allegations of cash for honours, then they get accused of a conspiracy to pervert the course of justice over it and now they seem to be involved in another conspiracy to cover the conspiracy.

“The effect of this leak has been to give the police more ammunition of an attempted cover-up.”

Yesterday Geoff Hoon, the Europe minister appeared to indicate that it is possible that the investigation may result in a prosecution.

He told ITV1 that the Attorney-General should make sure the legal process should happen without having a series of revelations that “clearly might well jeopardise the fair conduct of a trial”.

Times Recommends

• How I lost the gift of joy for a while
• Why Ann Widdecombe has got it wrong
• Alas, it’s the end of the road for petrolheads