A perjury trial has been shown video footage in which Tommy Sheridan allegedly says he made a "mistake" by admitting to visiting a swingers club.
Mr Sheridan's former colleague, Colin Fox, told the High Court in Glasgow that the off-camera voice making the comment was that of the former MSP.
Mr Sheridan and his wife Gail, both 46, are on trial accused of perjury.
The couple deny lying during his successful defamation case against the News of the World.
Mr Sheridan won £200,000 in damages after the newspaper printed allegations about his private life, claiming that he was an adulterer who had visited a swingers' club.
After a police investigation, Mr and Mrs Sheridan were charged with perjury.
The video footage was played during evidence from Mr Fox on day four of the trial.
The video was said to have been filmed in the days after an emergency meeting of the SSP executive about the revelations in the News of the World.
It was obtained by the News of the World following Mr Sheridan's successful libel action against the newspaper.
In the video shown to the jury, Mr Sheridan allegedly talks about going into the emergency meeting and addressing its membership.
A man's voice was heard to say: "They want me to come to a meeting that night to explain myself and this is where I make the big mistake."
Mr Fox identified both Mr Sheridan, his friend of 30 years, and George McNeilage, who was Mr Sheridan's best man, in the video.
The voice, said to be Mr Sheridan, is then heard to say he made the biggest mistake of his life by confessing something in front of 19 people.
Mr Fox said he was "disappointed" by the emergence of the video.
Earlier in his evidence, Mr Fox told the court how Mr Sheridan had asked him to lie on his behalf.
The trial previously heard that at a meeting of the SSP executive committee, on 9 November 2004, Mr Sheridan allegedly admitted twice visiting a swingers' club.
One of the charges he faces is that he attempted to persuade Mr Fox to commit perjury shortly before the 23-day legal action got under way in 2006.
The SSP had not wanted to hand the executive committee minutes to the courts and one member was jailed for contempt of court over the issue, after which the party handed over the minutes.
Mr Fox, a former Lothians MSP, said he met Mr Sheridan at the Beanscene cafe near the Scottish Parliament on 18 June 2006, where Mr Sheridan requested that he lie.
He said: "The minutes had already been handed in by this stage and Mr Sheridan asked me to send a statement to his solicitor saying that the minutes, in effect, were false, that he had not admitted to attending a swingers' club and that those people who had said he had admitted to it were mistaken."
Advocate depute Alex Prentice QC asked whether he was prepared to do what Mr Sheridan asked.
He replied: "No. I told him it was a train wreck of a strategy.
"He was asking me to send a statement to his solicitor disowning my party, disowning those minutes. I told him I was not prepared to do it."
Mr Fox told the court that he and party colleague Allan Green met Mr Sheridan at the Golden Pheasant pub in Lenzie on 12 May 2006 and tried to persuade him to drop the action against the News of the World but they were not successful.
The SSP leader later told the court: "That executive committee of 9 November 2004 was the SSP's 9/11. It was when our totem came crashing down. We would remember that meeting for the rest of our lives."
Mr Fox also told how he saw a newspaper article where Mr Sheridan described him as a scab in the days following Mr Sheridan's successful defamation case.
He said the description made him feel "sick to the stomach".
The court was also told that, as well as visiting the swingers' club, Mr Sheridan had an affair with a member of the SSP, Katrine Trolle.
Duncan Rowan, the former regional organiser of the SSP for the north-east of Scotland, then told the court he had informed the News of the World about the affair to try to protect another woman, Fiona McGuire, who the newspaper thought was having an affair with Mr Sheridan.
The 37-year-old, who resigned from the party and left Scotland after going to the newspaper, said Ms McGuire had tried to kill herself after she was approached by the newspaper in connection with allegations of a "four-in-a-bed" orgy with Mr Sheridan.
He said he went to the newspaper the day after the emergency meeting because he blamed himself for the "fragile" woman's suicide attempt and had been told by Ms Trolle that she had been having an affair with Mr Sheridan.
He said: "I had to do something to recover the situation. It was because Katrine had said to me on previous occasions that she was having an affair with Tommy Sheridan.
"I believed they had the wrong person, I believed I knew who the right person in the story was."
Mr Rowan said he was wracked with guilt after the article was published and told the court he had left Scotland because he "wanted to get away from the mess".
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.
The trial, before judge Lord Bracadale, is due to last between two and three months and is expected to become the longest perjury case in Scottish legal history.