Police are investigating claims that the wife of Tommy Sheridan committed perjury during her husband’s libel trial against the News of the World.

Detectives are expected to interview Gail Sheridan as part of a widening investigation into allegations of perjury during the trial against the tabloid newspaper, during which Mrs Sheridan won plaudits for her style and composure in the witness box.

Telephone records of Mrs Sheridan, who wept as she said she would have murdered her husband had he cheated on her, are also expected to be examined by detectives.

The Times can disclose that Lothian and Borders Police have doubled the number of officers assigned to the case to 20 detectives and are said to have gathered a huge volume of evidence that could take them months to examine. They are also said to be considering formally expanding their investigation to include the possibility of charges of conspiracy to pervert the course of justice, as well as perjury and conspiracy to commit perjury.

Although it may be weeks before detectives interview Mr Sheridan and his wife, sources said that there had been a marked increase in police activity over the past two weeks.

At least ten of Mr Sheridan’s former colleagues in the Scottish Socialist Party, including two former MSPs, have been interviewed by police over the past few days.

Mr Sheridan’s courtroom battle against the News of the World transfixed Scotland and led to him and his wife becoming at a stroke one of the country’s most glamorous couples.

The former leader of the Scottish Socialist Party, who represented himself after sacking his legal team, was awarded £200,000 in damages at the High Court in Edinburgh last August. The jury ruled that he had been libelled in articles claiming he had cheated on his wife, visited swingers’ clubs and had taken part in orgies. The newspaper is appealing against the verdict.

Crucial to Mr Sheridan’s case was the evidence of his wife, who described him as a loving family man who doted on his young daughter and had a fixation with Scrabble and sunbeds.

She said that, had Mr Sheridan been unfaithful, he would have been “in the [River] Clyde with a piece of concrete tied around you and I’d be in court for your murder”.

The judge said at the end of the case that he was concerned about “contradictory evidence” given by witnesses. In October prosecutors in Edinburgh instructed police to begin a formal perjury investigation.

In a new development, The Times has been told that officers are also keen to examine telephone records, including those of Mrs Sheridan, for dates when the News of the World said that Mr Sheridan was taking part in group sex.

Mrs Sheridan told the court that she had checked her diaries for the dates in question, adding: “Every weekend when he was supposed to be hanging from the chandeliers, he has been with me.” However, at least one person interviewed by police has claimed that on one of the nights in question Mrs Sheridan was not with her husband and was trying to reach him by telephone.

Detectives are also believed to be considering using technology that tracks where mobile telephone calls were made.

Officers have told those interviewed so far that they have been spoken to as “witnesses” rather than suspects.

Mr Sheridan, who lost his seat in the Scottish Parliament in this month’s election, said yesterday that both he and his wife had had “absolutely zero” contact with police.

He has claimed that he is the victim of a conspiracy by the Security Services, and earlier this year reported to police the discovery of a suspected bugging device in his car.

He said last night: “I’ve received no informal, formal or any other contact, other than press speculation, which has been increasingly hostile towards me.”

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