Last Friday the Prime Minister was questioned for a second time by Scotland Yard detectives investigating the alleged sale of peerages to Labour party donors.
A No 10 spokesman confirmed this morning that Mr Blair was questioned at Downing St by Metropolitan Police detectives.
The interview lasted for less than an hour.
The police had requested a news blackout, which is why the information has only been released today.
Last Friday Mr Blair was still trying to reach a compromise with Cabinet and Commons colleagues over a possible exemption for Catholic adoption agencies from the Sexual Orientation Regulations.
He had been in favour of an opt-out for the Catholic agencies, but divisions in his Cabinet and protests from his own MPs led him to concede that there would be no exemptions to the regulations, which outlaw discrimination on the grounds of sexual orientation when accessing goods and services.
On Monday, Mr Blair announced that adoption agencies would be given until the end of 2008 to adjust to the regulations, due to become law in April.
On Tuesday one the Prime Minister’s closest allies was arrested on suspicion of conspiracy to pervert the course of justice.
Lord Levy, who is Mr Blair’s special envoy to the Middle East, was first arrested last July and was released on bail in connection with the Metropolitan Police investigation.
Suspicion of perverting the course of justice is the reason police gave for arresting another close aide to the Prime Minister, Ruth Turner, earlier this month.
The “cash for honours” scandal started when it emerged that wealthy donors to the Labour party had been encouraged to loan rather than donate money to the party.
Several donors were nominated for peerages and then rejected by the House of Lords Appointments Commission.
Donations have to be publicly declared, whereas loans at a commercial rate do not, leading to accusations that Lord Levy, who is the major fundraiser for the Labour party, had instructed donors not to declare the loans to the commission.
On 14th December 2006, Mr Blair became the first sitting Prime Minister to be questioned by police as part of a criminal investigation.