Mr Baldassara and Mr Sheridan are no longer friends

Anvar Khan also claimed she saw Mr Sheridan taking part in group sex with another woman and his brother-in-law.

The accusations were made at the Court of Session in Edinburgh where Mr Sheridan is suing the News of the World newspaper for defamation.

The Sunday tabloid published a series of stories about the MSP's sex life which he claims were untrue.

On the fifth day of the civil action, Ms Khan, 38, claimed she flew from London to Glasgow to meet up with Mr Sheridan, his brother-in-law Andrew McFarlane and Scottish Socialist Party member Catrine Trulle in November 2002.

She testified that Mr Sheridan took part in a threesome with Mr McFarlane and Ms Trulle before driving to a swingers club in Manchester, where Mr Sheridan paid the entry fee for the party of four.

"It was very much a place where people go to have casual sex but it was not a sexy environment," she said.

'Open relationship'

Ms Khan told the court she first met Mr Sheridan in 1992 when she interviewed him in Saughton Prison, Edinburgh.

The jury heard she was working as a journalist for The Herald newspaper, while the MSP was serving a jail sentence for his role in the Poll Tax protests.

She said their "on-off casual sex relationship" continued after Mr Sheridan married his wife, Gail, in June 2000.

Ms Khan said: "He always maintained he had an open relationship.

"My position is that it is the married man who takes the vows. I was single."

Ms Khan told the court she first met Mr Sheridan in 1992

Earlier on Monday, the court heard from a friend of Mr Sheridan's who said he almost quit working for the Socialist MSP after hearing about a stag night party in a Glasgow hotel.

Keith Baldassara, 49, said he considered leaving his post after Mr Sheridan's brother-in-law spoke about a "night of madness".

Mr Baldassara told how he heard about the stag night party held for Andy McFarlane, who married the sister of Mr Sheridan's wife, Gail.

He said: "He (Mr McFarlane) just commented about an event in a hotel which was madness. He just said it was a night of madness.

"He said there wasn't enough room in the bed and there was somebody specially flown in from Birmingham for the night."

'Consenting adults'

Mr Baldassara said he later spoke to Mr Sheridan about the party and the politician admitted he was at the stag night, but that was all.

"He said he didn't participate. I accepted that," he said.

"He said he was present but confirmed to me that a lady from Birmingham was brought in but he said it was consenting adults who were happy to be involved.

"I didn't have any issue with that. I never had an issue with that. My main concern was that it was paid for. He assured me that it wasn't."

The court heard the two men are no longer friends though Mr Baldassara is still the MSP's parliamentary case worker.

The Glasgow councillor also said he had been told, by Mr Sheridan, of a visit to a swingers club in Manchester accompanied by Ms Trulle.