Former Tory leader Michael Howard last night announced he had been interviewed by police probing the cash-forhonours affair.
Mr Howard said he had "agreed" to be interviewed, and had not been arrested or questioned under caution.
In a statement last night, Mr Howard said: "In response to a request from the police, I agreed to be interviewed by them in connection with their inquiries into nominations for peerages.
"The police emphasised that they wanted to interview me as a witness and that I was not under suspicion of having committed any criminal offence. The interview was not conducted under caution. It took place this morning at my home in London."
A Tory Party source said the Scotland Yard investigation, led by Deputy Assistant Commissioner John Yates, was "clearly looking into people nominated for peerages by Michael Howard and Tony Blair".
"We have always expected that both would be interviewed in due course," the source added.
A Downing Street spokesman confirmed last night that Mr Blair had not been contacted by police over the affair. Mr Howard's announcement will heighten speculation that the Prime Minister faces a quizzing by detectives soon.
One of Mr Blair's top aides, 36-year-old Ruth Turner, was questioned under caution last month.
Ms Turner, who took on her role as director of Government relations at Number 10 in May last year, is believed to have been asked about emails and documents relating to the inquiry.
Earlier this month, leading Tory donor Bob Edmiston was reported to have been questioned under caution.
Mr Edmiston, who made a multi-million pound fortune importing cars, loaned the party £2 million.
He was among nominations for a peerage blocked by a Lords appointments watchdog in the summer, although that was in relation to tax issues.
The cash-for-honours investigation was sparked by claims earlier this year that wealthy Labour backers were being rewarded with seats in the House of Lords.