On a damp day in the northern French city of Lille, where an early-morning flurry of snow has turned to drizzle, there is only one subject of conversation – and it is not the inclement weather.

The talk is of politics, power and pimping, and whether former presidential hopeful Dominique Strauss-Kahn was simply a man with an insatiable penchant for sex or – unlikely as it seems – a key figure in an “international” vice ring.

On Monday the former head of the International Monetary Fund will go on trial on a charge of proxénétisme aggravé, which translates as aggravated procuring for the purposes of prostitution. The case is unprecedented in France, where strict privacy laws have until now largely prevented light being shone into the darker, sleazier corners of politicians’ personal lives. It is also seen as a test of French voters’ broad-mindedness about their politicians’ sexual proclivities, and evidence of an austere new morality in a country that has long mocked “Anglo-Saxon puritanism”.

L’affaire du Carlton, named after a hotel at the centre of an alleged prostitution network, and its colourful cast of accused – including a police commissioner, the owner of a chain of brothels named Dodo la Saumure (Dodo the Pimp), a barrister, two luxury hotel directors and several freemasons – make for a salacious tale. The summary of allegations runs to 240 pages, but in short the prosecution claims Strauss-Kahn took part in, and may have even organised, parties held in Belgium, France and the US where female escorts were paid to have sex with guests, himself included.

While neither prostitution nor paying for sex are illegal in France and the French Sénat – the upper house of parliament – rejected a government attempt to criminalise prostitutes’ clients last September, proxénétisme covers a wide range of crimes, including aiding, abetting, organising, encouraging or assisting in the prostitution of others. This is the basis of the charge against Strauss-Kahn and his 13 co-accused, all of whom have denied the charges.

Strauss-Kahn, 65, has admitted a penchant for “libertine” parties and having sex with a number of women. He denies knowing that women were paid for their services and has described the charges as “dangerous and malicious insinuations and extrapolations”. Supporters say Strauss-Kahn is the victim of what they describe as a new, feminist-led moral crusade and that, while his behaviour was ill-advised, it was not criminal. Critics argue that the allegations are part of a pattern of abusive behaviour, and point out that Strauss-Kahn has been accused, though never convicted, of predatory sexual behaviour in France and the US on several occasions. Even the local prosecutor, who advised dropping the case, argued that the evidence against Strauss-Kahn was flimsy. The three judges – two of whom are women – ignored him and ordered a trial.

Few, if any, believe that Strauss-Kahn will be locked up, but over the next three weeks the man once widely expected to become French president will have his sexual proclivities paraded and examined in excruciatingly embarrassing detail. “Much time will be spent discussing whether this or that sex act is deviant or not, and what the girls involved in the case would or would not do if they were or were not prostitutes,” said Didier Specq, retired court correspondent for the Voix du Nord local newspaper.

“It’s not a particularly important case in legal terms. The involvement of DSK has given the case an importance out of all proportion to the accusations, and some of the accusations seem far-fetched to say the least. This is about politics and media and about moral judgments.” After all, Specq added: “Everyone knew DSK had a rampant sexual appetite.”

It’s true that French people have the impression they live in a very liberal society when it comes to sex Didier Specq

Specq has written a book on the case called DSK chez les Ch’tis, (Ch’tis being a nickname for those who live in France’s most northerly region and featuring in the title of the recent hit film Bienvenue chez les Ch’tis). “It’s true that French people have the impression they live in a very liberal society when it comes to sex. This is the idea we have of ourselves, and it isn’t exactly correct,” said Specq. “It’s true the morals of the 1950s have long gone out of the window, but a new morality has come in by the back door.”

Strauss-Kahn no longer has a political career to lose. His presidential hopes came to an abrupt and definitive end in 2011 after he was removed from an Air France flight as it was about to leave New York and accused of forcing a Guinean-born chambermaid, Nafissatou Diallo, to perform oral sex at the city’s Sofitel hotel. While some in France still believe he was the victim of a honeytrap to prevent him running for president, the case stripped away some of the aura of impunity and untouchability surrounding Strauss-Kahn at home. Criminal charges against Strauss-Kahn were subsequently dismissed. He later settled a civil lawsuit filed by his accuser.

The Hotel Carlton investigation had begun shortly before Strauss-Kahn’s arrest in America and was initially a local affair. Lille police had just set up a dedicated proxénétisme investigation team when they were tipped off that the hotel’s head of public relations was bringing together “well-connected men”, and young girls who worked as prostitutes.

The Hotel Carlton in Lille, centre of a sex-party case that will expose DSK to further scrutiny. AFP/Getty Images Photograph: AFP/Getty Images

Arrests were made, searches and raids carried out, but the affair remained parochial until a number of women mentioned Strauss-Kahn’s presence at swinger parties in Paris, Brussels and Washington, home of the IMF.

Christine Delphy, a feminist sociologist and writer, believes the Carlton trial shows attitudes are changing but, she says, “only marginally and very slowly”. “I still hear people claiming the Sofitel incident was a conspiracy or blaming it on American puritanism and defending what DSK did with the ‘private life’ argument,” said Delphy. “This is France, a country where many white politicians asked how it was possible that a black, immigrant chambermaid dared to make a complaint against a powerful man, where Nafissatou Diallo was treated as a liar and a gold-digger. A male commentator said what happened was simply a case of the master having his way with the servant.

“The Carlton case may show there has been a small degree of change, but these macho attitudes have not changed much. I’d be astonished if there is a conviction.”

Walking around Lille, Specq gives a guided tour of the trial hotspots, including the four-star Hotel Carlton in which, as it happens, Strauss-Kahn has never set foot, and the palais de justice into which he will step tomorrow, a concrete building whose very drab, grey austerity seems a stark reminder of a would-be president’s fall from grace when the keys of the Elysée palace were within reach.

“This story could have come straight out of Balzac,” Specq said. “We can ask ourselves why a man who is so powerful has sexual relations so dangerous that could open him up to blackmail and pressure. That’s stupid, not criminal. What is actually on trial here is Strauss-Kahn’s morals.”