Ruth Turner, Tony Blair's "gatekeeper", has been questioned by Scotland Yard detectives for a third time in the cash for peerages inquiry, it emerged yesterday. Officers cross-examined Ms Turner, 36, for two hours as she answered her bail on Tuesday at a London police station.

The Prime Minister's director of government relations was first questioned under caution in September, reportedly in relation to emails uncovered by the police during a search of Downing Street computer and paper files.

However, last month the stakes were raised when she was arrested on suspicion of perverting the course of justice. She has denied any wrongdoing. On Tuesday, Ms Turner was again released on bail, pending further inquiries. She was not arrested and not charged.

Scotland Yard refused to confirm the name of the woman interviewed, but said she had been arrested at her home a month ago.

A spokesman said: "On January 19, a woman, known as D, was arrested at her home address in London by Metropolitan Police officers in connection with alleged offences under the Honours (Prevention of Abuses) Act 1925 and also on suspicion of perverting the course of justice.

"She was taken to a London police station where she was interviewed and later bailed to return pending further inquiries. She returned on bail on February 20, was reinterviewed and then rebailed pending further inquiries."

No 10 made no comment on the latest development.

Ms Turner's arrest at her London home last month took the 11-month investigation on to a new level as it was the first indication that detectives were looking into the possibility of a cover-up.

At the time, senior Labour politicians denounced the Metropolitan Police's tactics as heavy-handed.

The aide's arrest was followed a week later by a second interview for Mr Blair himself, who was not arrested or put under caution. Then the PM's personal fundraiser Lord Levy was arrested for a second time, this time under suspicion of conspiracy to pervert the course of justice.

Around 90 people have been questioned by officers from Scotland Yard's Specialist Crimes Directorate, including First Minister Jack McConnell, who was quizzed about his nomination of a peerage for Lord Boyd, former Lord Advocate, his one and only nomination.

Last night, Angus MacNeil, the SNP back bencher whose complaint last March initially sparked the police investigation, said: "This is another dark day for Tony Blair and his Downing Street administration. What would have seemed inconceivable a year ago, for the Specialist Crime Directorate to be interviewing those in Downing Street, is almost acceptable today."

The Western Isles MP added: "Blair's ship seems to be sinking and he is going to have to search for a life raft."

There have so far been no charges in relation to the allegations that honours were offered to wealthy Labour supporters in return for loans to bankroll the party's 2005 General Election campaign. All those questioned deny wrongdoing.

Earlier this month, the Crown Prosecution Service announced there was insufficient evidence to prosecute Des Smith, an east London headteacher, over "indiscreet" comments he made to an undercover reporter about how donating money to the government's City Academy programme could lead to donors being recommended for an honour.