The great 19th Century Scottish judge Lord Cockburn, once observed that a case he had witnessed was “a personified compound of avarice, indecency, official insolence and personal cowardice, great law and practical imbecility”. To that impressive list, he might have added this week: brazen arrogance, political back-stabbing, treachery and betrayal. All have been on display in the case that Mr Sheridan has brought against the News of the World, and which has had queues forming at dawn outside Court No 6.

Here, one of Scotland’s most singular politicians is fighting not just for his reputation, but for the future of his party. He is suing the newspaper for £200,000 after it printed a story about an unnamed Member of the Scottish Parliament who was said to have visited a swingers’ club in Manchester, where he took part in drink-fuelled orgies that included the full range of tabloid favourites: three-in-a-bed sex sessions involving a series of women, none of whom was his wife. That MSP, it now transpires, was Mr Sheridan.

The founder and, until he resigned to fight his case, convener of the SSP, whose tanned good looks and fiery radicalism have made him a media star, arrives each morning smiling for the cameras, accompanied by his glamorous air-hostess wife, Gail, looking, as one onlooker put it, like someone out of Footballers’ Wives. Inside, the drama is almost its soap opera equal.

Last week Mr Sheridan fired his legal team and is now pursuing the case himself. He stands, wigless and unrepentant, in front of Lord Turnbull, one of Scotland’s most senior judges. Mr Sheridan asks for, and is given, a lectern, from which he trades legal badinage with the paper’s counsel, Michael Jones, QC, addressing the jury as if they were prospective voters rather than the 15 men and women who hold his fate in their hands. Verbose, self-confident, occasionally truculent, but punctilious when it comes to addressing the judge, Mr Sheridan is holding his own.

Yesterday, to add the final element of legal surrealism, he was called as a witness, to be cross-examined by Mr Jones. Strolling over from the legal benches to the witness-box to affirm his oath, he said: “If you hadn’t called me, I would have called myself.”

Mr Sheridan makes great play of his status as a happily married man, true to his socialist ideals, and a teetotaller. Mr Jones loses no opportunity to remind the jury that the case involves the most damning charge a politician can face: hypocrisy. He lets slip phrases such as “prostitution, pornography and lap-dancing”.

In return, Mr Sheridan seeks to mock Mr Jones’s case, his evidence and his legal skills, referring to the paper routinely as the “scab reactionary representative of the boss class”, and suggesting that Mr Jones is pursuing a series of red herrings. “You’re confusing me, Mr Jones,” he said at one point. “I don’t know whether you’re confusing yourself.”

Then, later: “Mr Jones, even by your standards that’s a ridiculous question.”

“There’s no need to be rude to me,” came the pained response. “I’m not being rude to you, but your line of questioning is not particularly courteous.” Then: “Are you grinning at me, Mr Jones?”

“It is not my job to display emotion, Mr Sheridan, and I apologise for that.”

At one point Mr Sheridan apologised to the judge for implying that he might be “pompous”. “Sometimes judges are pompous,” he said, then, turning to Mr Jones, “but so are QCs.”

At the heart of the case, however, are the raw politics of the SSP and a party minute recording a meeting of its executive shortly after the News of the World had published its exposé in November 2004. At this meeting, Mr Sheridan is said to have admitted visiting the club, but went on to claim that there was no evidence to prove it. He denies that he said any such thing and argues that the minute is a “dodgy” record of what was said.

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