A former News of the World columnist has told the Tommy Sheridan perjury trial that she had sex with the former MSP while he was married.
Anvar Khan also told the High Court in Glasgow she went with Mr Sheridan and three other people to a swingers' club in Manchester in the autumn of 2002.
Mr Sheridan and his wife Gail, both 46, are accused of perjury.
They deny lying at his successful defamation case against the News of the World in 2006.
The former Scottish Socialist Party (SSP) leader 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.
Following a police investigation, Mr Sheridan and his wife were charged with perjury.
Freelance journalist Ms Khan, 43, told the court that she first met Mr Sheridan in the course of her work around 1992 and went on to have sex with him on several occasions.
She said that Mr Sheridan had phoned her after she moved from Scotland to London, telling her he had visited a sex club on his own and asking her to go with him.
She said the telephone conversation took place around September 2002.
"He said he had been to a sex club, or a swingers' club. I was surprised. He said: 'I went on my own'," she said.
"He wanted to know if I would go with him and a couple of his friends to this club again.
"I was surprised. I think I may have said: 'Didn't anyone recognise you?'
"I didn't exactly say I was staying in washing my hair. I said it was interesting."
Ms Khan then told the court that Mr Sheridan made arrangements for the trip to the club and she was to fly to Glasgow at the end of September, adding: "I think it could have been September 27."
She said she had become "mates" with Mr Sheridan and asked him for advice on campaigning, as well as looking to him for stories for the newspapers she worked for.
She said there was initially "a very flirtatious atmosphere" between the two and they "had a snog" before making "a date for sex" at his home in the Pollok area of Glasgow in 1992.
She told how she had sex with Mr Sheridan beneath a picture of Communist revolutionary Che Guevara.
She said: "What struck me was pictures of left-wing intellectuals on the walls. We went into his bedroom, there was a large picture of Che Guevara above the bed, and we had a shag."
Ms Khan, who is now married but told the court she preferred to use her maiden name during proceedings, said she next saw Mr Sheridan around 1999, or 2000, adding that she "believed" he was now married to his wife Gail.
She said he visited her home in the Kelvindale area of Glasgow on two occasions, once with one person, and once with his brother-in-law Andrew McFarlane and a woman named Suzie.
Advocate depute Alex Prentice QC asked her: "Did you have sexual intercourse?"
She replied: "Yes".
He then asked: "Was anyone else present?"
She said: "Yes".
She said that on the second occasion she had asked Sheridan to bring a "carry-out" with him, saying that he had turned up with around 20 miniature bottles of wine of the type given out on aeroplanes.
She told the court: "I remember being quite taken aback that he didn't understand that a carry-out meant full wine bottles."
Under cross-examination from Mr Sheridan, who is representing himself, Ms Khan was asked if she had benefited from the allegations about him appearing in the press.
She replied: "I think it would be the opposite. I have been box-office poison. I certainly have not had much work in Scotland."
Ms Khan told the court she had a meeting with the editor of the Scottish News of the World, Bob Bird, in which she said she felt "blackmailed" into co-operating with the newspaper's lawyers in Sheridan's defamation action.
She said she had felt her job had been under threat but she "stuck to her guns" and hadn't worked with either side in the action, but had given evidence only because she had to.
'Pursued for weeks'
Ms Khan also said she had been "pursued for weeks" by the Daily Mail, who also wanted her to give them an exposé on Sheridan, but had never been paid for the story, or benefited from it in any way.
Mr Sheridan said: "The mask you have brought with you to this court is beginning to fall off. You are here to bolster your friends at the News of the World and bolster their stories and their lies about me."
She replied: "Your assessment is neither realistic, nor is it fair."
Mr Sheridan asked her about alleged inconsistencies between her testimony in 2006 and the account she had just given in court.
He said in 2006, she had said Sheridan had arranged for his brother-in-law Andrew McFarlane to meet her at Glasgow airport before visiting Cupid's swingers' club, and she had been concerned about how he would recognise her.
But she had told the court today he had been to her house before the trip was arranged.
Ms Khan said Sheridan had told her at the time it would either be Mr McFarlane or another friend whom she had not yet met who would pick her up.
She also said she had not been been able to go through her evidence before the case, or "scientifically" work out the dates or exact sequence of events as she had done for the perjury case.
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 Lord Bracadale, continues.