It has become a ritual: the long queues under the vast marble arches of the Palais de Justice, the bustling lawyers, the traffic jams by the Seine, the bored policemen, the occasional confused tourist wondering what all the fuss is about. For over a month, the "Clearstream" trial, the culmination of an extraordinarily complex series of political, financial and legal investigations and manoeuvres, has gripped France.

Today, the crowded hearings in the high court's Prémière Salle ended. But the Clearstream affair was never going to end in an ordinary trial.

In the dock, with four others, was Dominique de Villepin, the urbane, aristocratic former prime minister and foreign minister, best known outside France for his powerful oratory during debates at the United Nations in New York in the run up to the 2003 Iraq War.

De Villepin was accused of trying to cause catastrophic political damage to the career of Nicolas Sarkozy, the current president, by arranging for (or at the very least allowing) a forged list of account holders to reach investigating judges. The accounts were supposed to hold ill-gotten gains from kickbacks or the proceeds of organised crime, and the list included the name of De Villepin's arch-rival, as well as those of scores of other top political and business establishment figures.

The president was not physically in the courtroom – though he was represented by lawyers as one of 40 plaintiffs who had brought the case – but was present in spirit nonetheless. Much of the defence of De Villepin, for whom prosecutors have demanded an 18-month suspended prison sentence and a €45,000 (£41,000) fine, is that he is the innocent victim of a political vendetta.

"I am here because of one man … Nicolas Sarkozy promised to hang me from a butcher's hook. I see that the promise has been kept," he said early in the trial, referring to a reported comment from Sarkozy.

It is not just the blows traded across the courtroom floor by the representatives of the two men that have provoked the interest in France, however. The daily hearings, in a magnificent neo-gothic wood-panelled courtroom, have been a window into an astonishingly murky world of spies, kickbacks and political dirty tricks.

The affair has its roots in a 2001 investigation by French judges of alleged bribes paid during a $2.8bn (£1.7bn) sale of French frigates to Taiwan 10 years earlier. The judges were sent documents by an anonymous informant with the details of thousands of accounts supposedly held at a Luxembourg-based financial securities clearing house called Clearstream, which was supposedly linked to vast organised crime syndicates and alleged kickbacks from the frigate deal.

Many of the accounts were held by former and serving ministers, captains of industry and other senior figures. Two names — Bocsa and Nagy — jumped out. Together they composed the full original family name of the French president, the son of a Hungarian aristocrat immigrant. When it became clear the lists passed to the judges were forgeries, the focus of the investigations switched to tracing their provenance.

The source was eventually revealed to be Jean-Louis Gergorin, former executive of aerospace group EADS, renowned defence strategist and fully-fledged member of the great and the good. Gergorin admitted sending the documents to the judges but claims he did so at the request of his friend De Villepin, then locked in a vicious battle to succeed President Jacques Chirac as the leader of the French mainstream right.

The account lists were allegedly falsified by a Lebanese computer specialist, convicted fraudster and part-time "source" for French intelligence called Imad Lahoud, who worked for Gergorin.

He too has been sitting quietly in court. His lawyer mounted an unusual defence last week, telling the court that his client "was [and] is a liar" and begging the five judges' "pardon" for his "torrent of lies". Also in the dock is a young accountant who allegedly stole crucial documents from Clearstream and the reporter who received them from him.

Among the witnesses heard have been two of France's highest-ranking former spies: General Phillippe Rondot, a respected veteran of espionage who captured the notorious terrorist Carlos the Jackal, and Yves Bertrand, head of the secret police for 12 years until 2004, whose diaries were seized as part of the investigation.

Rondot was asked by De Villepin to investigate the allegations against his rival and told the court that Sarkozy had appeared of particular interest to the then foreign minister. Rondot's previously impeccable reputation has also been somewhat tarnished by the revelation that for some time he apparently thought that Lahoud might lead him to capture Osama bin Laden.

As for Betrand, rather than reveal anything about the Clearstream affair, his diaries were found to contain hundreds of pages of scribbled notes on the sexual tastes of senior politicians and unflattering references to Sarkozy's second wife, Cécilia.

De Villepin, 56, has argued that he is the victim of a political vendetta and that he acted entirely properly as a minister at the time in having the false list of accounts investigated as it could have posed or indicated a risk to national security.

He and Sarkozy have never tried to hide their mutual enmity. The two represent polar opposites. Not only is there the physical contrast between the tall, slim, silver-haired De Villepin and the short, hyperactive Sarkozy, but there is a cultural gulf too. De Villepin, a blue-blooded career diplomat educated in elite schools who still found time while a senior minister to write volumes of passable poetry and lengthy histories of Napoleon Bonaparte represents a France that disdains Sarkozy.

The president is a lawyer who attended neither establishment schools nor universities, is seen as painfully and un-Gallically pro-American, does not drink, likes hamburgers, flaunts his friends' wealth and whose lack of interest in the arts is well-known. The pair also represent different wings of the French right.

"Dominque de Villepin incarnates the traditional values of the French conservatives: the greatness of France, social justice, democracy, equality and cultural exchange," said Anne-Béatrice Delange, 60, who has queued every day to show her support for the former prime minister in court. "Sarkozy incarnates the opposite."

But though the affair has dominated the press – the Le Monde newspaper is to publish an eight-page supplement on the affair tomorrow — it is not clear how much impact it has had more broadly. One recent poll showed that though 39% of the population said they had talked about Clearstream in recent weeks, the affair was ranked last out of 15 concerns, well below the recent wave of staff suicides at former state monopoly France Telecom, or the president's failed bid to parachute his 23-year-old son into a powerful post as president of the management board for La Défense, Paris' main business district. "It's just too complicated for most people," said Frédéric Dabi, of pollsters IFOP.

The stakes for De Villepin, who sported a smooth smile, impeccable suit and a permanent tan throughout the hearing, are high. If he is found innocent, the trial could be the "trampoline" which relaunches his flagging political career, Dabi said. If he is found guilty, it could be its "cemetery".

After today's hearing De Villepin said that he wanted "to turn the page … to look to the future … and to serve the French people in however they desire."

The judgement will not be delivered for several months.

• This article was amended on 24 October 2009. The original headline and standfirst referred to the frigate deal with Taiwan, but this was not part of the Clearstream trial, only part of the background to it. These references have now been removed.