The 62-year-old politician and his multi-millionaire heiress wife Anne Sinclair tried to counter-attack on Monday, threatening to sue media reporting the latest rumours on the state of their marriage for invasion of privacy.

But Strauss-Kahn has now been linked to a judicial inquiry into an alleged illegal prostitution ring, and he still faces a civil suit from a New York hotel maid who claims he sexually assaulted her back in May.

Once seen as the favourite to oust Nicolas Sarkozy and win next year’s French presidential election, Strauss-Kahn is now an embarrassment to his Socialist Party, shunned by the campaign and former close allies.

French media have revealed text messages allegedly sent by Strauss-Kahn to a businessman detained on suspicion of organising sex parties in restaurants and swingers clubs in Paris, Washington, Madrid, Vienna and Ghent, Belgium.

He has demanded to be questioned by the judges leading the inquiry, hoping to halt what his lawyers brand a “media lynching”, but some warn he could face charges if the case expands to cover alleged graft or influence peddling.

“DSK, a man alone,” declared the front page of the popular Le Parisien newspaper on Monday, over a picture of the formerly respected economist and global statesman wearing a dejected frown and a scraggy grey beard.

Once he was courted by dozens of senior figures, keen for a role in his expected future government, or hoping that some of the glamour and energy of his jet-setting lifestyle and glamorous celebrity marriage would rub off.  

Even after the shock of the US case — which collapsed after prosecutors came to doubt the testimony of the alleged victim but ended his IMF career — many stood by him, predicting an improbable comeback for their champion.

But now, with each week bringing new unseemly allegations, the small court of hangers-on who used to meet or telephone their champion at his elegant flat in Paris’s super-fashionable Place des Vosges has dispersed.

“We can see today he would have been a very vulnerable candidate,” said Pierre Moscovici, a former Strauss-Kahn confidant who has joined Socialist flag-bearer and new presidential favourite Francois Hollande.

Privately, many senior Socialists use harsher terms to describe their “betrayal”, while others are scrambling to distance themselves.

Former prime minister Michel Rocard boasts of having been the “first to say” Strauss-Kahn must be mentally unwell, and the mayor of Lyon, Gerard Collomb says he is “a friend, but not a friend I’d go on holiday with.”

Strauss-Kahn resigned as director of the International Monetary Fund in May, and returned to France in August after the US case collapsed, only to face new allegations.

First, a 32-year-old writer accused him of attempting to rape her in 2003 but, while prosecutors said there was prima facie evidence of sexual assault, the case was too old to pursue.

Now, he has been implicated in an entirely separate investigation into an alleged prostitution ring said to have operated out of luxury hotels in the northern French city of Lille.

Magistrates have already charged several leading local figures with organising the ring and there are suspicions that a construction company executive used his firm’s money to entertain guests at sex parties.

The press has also carried reports of Strauss-Kahn attending parties in a Paris hotel with Lille’s chief of police and the alleged kingpin of the ring “Dodo la Saumure”, who runs massage parlours in Belgium.