A former Scottish Socialist Party (SSP) colleague has told a court he was "heartbroken" when Tommy Sheridan admitted to visiting a swingers club.
Richard Venton said Mr Sheridan admitted at an SSP meeting in 2004 that he had visited the club in Manchester.
Mr Venton, 57, said he was "gobsmacked" by the admission which he described as "mind-boggling recklessness".
The former MSP and his wife Gail, both 46, are on trial accused of perjury. They deny the charges.
The Sheridans are accused of lying during Mr Sheridan's successful defamation case against the News of the World in 2006.
He won £200,000 in damages after the newspaper printed allegations about his private life, claiming he was an adulterer who had visited a swingers club.
Mr Venton, 57, was a founding member of the Scottish Socialist Party along with Mr Sheridan, and the two fought "shoulder to shoulder" for the socialist cause.
But at the High Court in Glasgow he told his former friend he was left "heartbroken" by the chain of events that led to Mr Sheridan's decision to take the News of the World to court.
Mr Venton said the former MSP told an emergency meeting of the party's top brass on 9 November 2004 he went to the club for "cheap thrills".
Mr Sheridan is said to have told the meeting he could "destroy" the News of the World's sex columnist Anvar Khan, with whom he allegedly visited the club, as a witness.
Recalling the meeting, Mr Venton said: "Tommy explained that he was the unnamed MSP that had been reported in the News of the World.
"He had been to this Cupid's club on a couple of occasions. It was retrospectively reckless and foolish."
The advocate depute, Alex Prentice QC, asked him if the SSP meeting had been a "kangaroo court".
He replied: "There was not a hint of kangaroos or any other marsupials in sight."
During his cross-examination Mr Sheridan, who is defending himself, suggested Mr Venton was part of "a plot to undermine me politically", and accused him of lying in his evidence.
Mr Venton replied that Mr Sheridan's tactic was "to throw muck about the courtroom and hope some sticks".
He said:" I have nothing to be ashamed of, I'm not lying.
"I know this court is near a fish market, but some of the red herrings you're throwing about are overpowering.
"What you have attempted to do today - but more fully at the previous trial - is sway the jury with your oratory and your charm and persuasiveness."
He said Sheridan's persuasive ability was a "curse" when used for the "wrong things".
Mr Venton said he gave evidence "under protest" in 2006, adding: "I did limit what I said. I saw myself not as a witness, but a hostage".
He said he had wanted "to save you from a crucifixion", saying: "I was trying not to give evidence that would damage you."
Earlier, the trial heard from journalist Ralph Barnett whose girlfriend used to share a flat with a woman Mr Sheridan is alleged to have had an affair with.
During the defamation case, Mr Sheridan said he had not had a sexual relationship with Katrine Trolle or stayed at her home in Dundee.
The trial earlier heard from Ms Trolle, who said she had sex with Mr Sheridan on several occasions between 2000 and 2004, including at her own home in Dundee and at his house in Glasgow.
Mr Barnett, a journalist with the Dundee Courier and Advertiser and the Dundee Evening Telegraph, told the trial he had seen Mr Sheridan arrive at the house and go upstairs with Ms Trolle, when he was visiting his girlfriend Ruth Adamson.
He said he had checked his diaries and believed the most likely date for the visit was 11 October 2004.
"At some point in the evening, Katrine told us she was going to meet Mr Sheridan," he said.
"She returned in her car with Mr Sheridan. We were aware of the car coming up the drive and we were aware of the door opening.
"Katrine and Mr Sheridan no more than poked their heads around the door. They went upstairs. They didn't come into the living room where we were."
Mr Barnett said he did not see Mr Sheridan again that night or the following morning.
He added that although there were three bedrooms in the house, the spare bedroom was "chaos", saying "it was just a box room, a storage room. There was never a bed set up there to my knowledge".
The court later heard from Mr Barnett's ex-girlfriend, Ms Adamson, who said she had also seen Mr Sheridan visit the house she shared with Ms Trolle.
The 30-year-old said the visit took place in late 2004.
She said: "He came round to the house one night. We were introduced, shook hands, there was brief chit chat, then Katrine and himself went upstairs. It was only the one time I saw him."
Ms Adamson told the trial Mr Sheridan would call her mobile phone to talk to Ms Trolle.
She said Ms Trolle did not have her own mobile phone, and the house did not have a landline, so she would let her friend use her phone.
She said: "I spoke to him a few times on the phone when he phoned for Katrine."
The trial also heard evidence from Scottish Socialist Party (SSP) member Steven Nimmo, who was the party's regional organiser for the Lothians area in 2004.
He was the 11th member of the party's executive to tell the court that he heard Mr Sheridan admit to visiting a sex club in Manchester on two occasions.
Mr Nimmo was not called to give evidence at the 2006 defamation action at the Court of Session in Edinburgh.
He said he met Mr Sheridan at Burger King in Edinburgh Waverley Station shortly before the action started.
He said: "I explained to Tommy Sheridan my position that I felt he should drop the case and, if I was called as a witness, I would tell the truth.
"We just went our separate ways, obviously Tommy decided to carry on with his action, and we are here today."
It is alleged that Mr Sheridan made false statements as a witness in his defamation action against the News of the World on 21 July 2006.
He also denies another charge of attempting to persuade a witness to commit perjury shortly before the 23-day legal action got under way.
Mrs Sheridan denies making false statements on 31 July 2006, after being sworn in as a witness in the civil jury trial at the Court of Session in Edinburgh.