POLICE investigating the court evidence in the Tommy Sheridan sex trial have spent the past three weeks probing the testimony of one of the case's key witnesses.

Officers for the Lothian and Borders force have conducted several interviews with Fiona McGuire, the former prostitute who claimed to have had an affair with Sheridan.

They have also tracked down people she claims were at an orgy with her and the Glasgow MSP, and have visited the Aberdeen hotel where she alleges the incident took place.

The events are the latest developments in the police investigation into whether perjury was committed during last year's notorious defamation trial involving Sheridan and the News Of The World.

The former leader of the Scottish Socialist Party (SSP) sued the Murdoch red-top after it alleged he was an adulterer who had attended a swingers' club. Several women claimed in court to have had affairs with the MSP, while nearly a dozen of his comrades in the SSP testified that he admitted to sex club visits.

However, the jury found in Sheridan's favour and he was awarded £200,000 in damages. But inconsistencies in the trial evidence have since prompted police to investigate the possibility that witnesses lied during the trial.

The Sunday Herald can reveal that the largest chunk of police time has been spent dealing with the court evidence provided by McGuire, who claimed to have had an orgy with Sheridan, as well as other casual encounters.

Detectives have been in the Aberdeen area for the past three weeks speaking to people linked to the alleged group sex session. Staff at the Treetops Hotel in the northeast have also been quizzed.

McGuire could not be contacted for comment last night.

Last week, witness Helen Allison, who claimed to have seen Sheridan have sex in a Glasgow hotel, was questioned for the second time. Anne Colvin, who also claims to have seen the same incident, will be interviewed today.

Meanwhile, the financial disputes between the SSP and Sheridan's new Solidarity party are heading towards resolution.

The row between ex-SSP treasurer Gordon Morgan and his former colleagues over a five-figure loan has been settled out of court, with the SSP handing over £21,500 to their one-time office bearer.

The Sunday Herald can also reveal the SSP has made a £40,000 profit from the sale of their offices in Glasgow.

The anti-capitalist party, which refused to release details of the December sale, sold the property to Loft Office Ltd for £153,000.