Ministers quizzed in cash-for-peerages probe

Tony Blair, the Prime Minister, was one of the few high-profile names not to have received a letter from police, heightening speculation that detectives are preparing to interview him in person. He is believed to have consulted the solicitors he used for the Hutton inquiry, Kingsley Napley.

Ministers, including Gordon Brown, the Chancellor, and John Prescott, the Deputy Prime Minister, were asked to submit any evidence they might have over claims that Labour's bankrollers were nominated for peerages. A source denied that either man knew anything about the loans.

"They [police] have simply asked those involved in the last election to declare formally in writing what they knew about the loans," the source said.

However, the Tory MP Andrew Tyrie, a former shadow Treasury minister, said:

"I find it surprising that a man like Gordon Brown, who is so obsessed with detail that colleagues have described him as a control freak, could have had no interest at all in knowing how the 18 million Labour spent was raised."

Others contacted by police include John Reid, the Home Secretary, David Miliband, the Environment Secretary, Jack Straw, the Leader of the Commons, Ruth Kelly, the Communities Secretary, and Ms Hewitt.

A Labour source described the approach by Scotland Yard as a "fishing expedition", adding that it was normal for police finishing an inquiry to have a "final trawl for evidence".

Alan Milburn, a long-time ally of Mr Blair who quit as health secretary in 2003, made it clear he was interviewed as a witness and not a suspect. "Following a request from the police, I have been interviewed as a witness. The police stressed I was not a suspect, and the interview did not take place under caution," he said.

Angus MacNeil, the SNP MP who prompted the police inquiry, said the extent of it showed how much trouble the government was in. "The credibility of the entire Cabinet now seems to be imploding," he said.

Three people - Lord Levy, Labour's unofficial fundraising chief; Sir Christopher Evans, a bio-tech entrepreneur and Labour donor; and Des Smith, a former adviser on education - have been arrested in connection with the inquiry. So far, no charges have been brought.