Scotland's first minister, Jack McConnell, was questioned by police investigating the cash-for-honours row, it has emerged.
He was interviewed as a witness during a trip to London on December 15th, not under caution. However, a lawyer was present as a precautionary measure.
His interview came the day after Tony Blair himself was questioned by Scotland Yard officers at Downing Street, although he was not interviewed under caution either.
It is believed Mr McConnell was questioned about the nomination for a peerage of Lord Boyd of Duncansby.
The lord advocate of Scotland was nominated in 2004 but the announcement was delayed because of the 2005 election. As a result, it has fallen within the scope of the police inquiry.
Scotland Yard is investigating claims that political parties, notably Labour and the Conservatives, offered seats in the House of Lords to wealthy businessmen in return for secret loans. All those involved deny wrongdoing.
On Friday, Mr Blair's director of government relations, Ruth Turner, became the fourth person to be arrested as part of the inquiry. She was released without charge and has protested her innocence.
Mr McConnell has headed the Labour-led Scottish executive since November 2001. It is thought he was contacted by police through the Labour party's lawyers.
About 90 people have so far been quizzed as part of the investigation, which was prompted by a complaint by the Scottish National Party (SNP) MP Angus MacNeil early last year.
Commenting on today's news, Mr MacNeil said: "The entire Labour party is becoming engulfed in this crisis of its own making.
"No-one believes for a second that Mr McConnell is directly implicated in securing cash for honours. But as a political party, Labour has financed campaigns north and south of the border with funding from people whom Tony Blair has subsequently ennobled or knighted."