Dubai: Nicolas Sarkozy, the former president of France who is trying to revive his political fortunes, was put under formal investigation on Wednesday in a corruption and influence-peddling case, news agencies reported.

The latest twist in a case that has gripped France came a day after Sarkozy was held for questioning by the police for 15 hours, the French media reported, an unprecedented indignity for a former French president. Sarkozy, a conservative who led the country from 2007 to 2012, was detained and questioned before being taken to a Paris court to meet with investigators. He was released after midnight, the French media reported.

The anticorruption authorities in France are looking into whether Sarkozy, abetted by his lawyer, Thierry Herzog, sought to obtain information from an influential appeals court judge, Gilbert Azibert, about investigations linked to the former president, including an inquiry into the financing of his 2007 election campaign. They are also investigating whether Sarkozy, Herzog and Azibert worked together to reward Azibert for his help in the case with a post in Monte Carlo.

Sarkozy, 59, has denied any wrongdoing and characterised the investigation as a politically motivated smear campaign. Sarkozy is the first former president in the history of modern France to be detained and questioned in police custody.

The decision to open a formal investigation could lead to a trial, legal experts said, and suggests that investigators believe they have enough evidence against the former president to link him to a crime.

The developments deal a heavy blow to hopes of a political comeback by Sarkozy, who has been urged by his supporters to make a run for president in 2017. While his critics accuse him of abusing his power, his defenders say he was merely engaging in the kind of political networking all too common in the cosy world of French politics.

The scandal comes at a time when France’s right is growing in surging. Marine Le Pen, the leader of France’s far-right National Front, could not have come up with a better script if she had written it herself. Throughout her campaign for the just-concluded European Parliament elections, Le Pen portrayed France’s mainstream politicians as corrupt and out of touch, a message that helped her party beat out both the governing Socialists and the opposition conservative party, the Union for a Popular Movement, or UMP.

As if on cue, the UMP, Sarkozy’s party, acknowledged that it had breached the legal spending limits in Sarkozy’s failed run for re-election in 2012 and that it had covered that up with false billing. Each day this week brought new headlines, including the resignation of the UMP’s leader. A lower-level official, tears in his eyes, appeared on television to take the blame.

She has gone so far to suggest that, in the absence of such cheating, the results of the 2012 presidential election might have been different — perhaps, for instance, she would have beaten Sarkozy in the first round and gone on to a victory over the now deeply unpopular Francois Hollande. She has also renewed calls for a dissolution of the National Assembly and for new legislative elections.

Le Pen, an adept campaigner, has played down her party’s past links to racism and xenophobia and articulated a populist message that resonates with French voters exhausted by years of economic troubles and insecure about their nation’s place in a rapidly changing world. With her sights set on a presidential run in 2017, she now faces a conservative opposition party racked by scandal and the governing party of Hollande, who has record-low approval ratings

Since he left office in 2012, Sarkozy has been forced to grapple with a series of court cases. Expectations that he could run again for the French presidency in 2017 have only served to intensify interest in the man once labelled “President Bling Bling” because of his perceived opulent lifestyle.

A long-running investigation in which two former Sarkozy aides have been charged by judges investigating alleged kickbacks on a Pakistani arms deal concluded when Sarkozy was budget minister. A shell company was allegedly used to channel kickbacks to then prime minister Edouard Balladur’s unsuccessful 1995 presidential bid, which Sarkozy helped run.

Magistrates are also probing whether a 2002 Karachi bombing that killed 11 French engineers was revenge for the cancellation of bribes secretly promised to Pakistani officials.

A criminal investigation is ongoing over a controversial €400 million (Dh2 billion) payout by the French state to tycoon Bernard Tapie in 2008.

Judges are looking at whether Tapie received favourable treatment in the case as a reward for supporting Sarkozy in the 2007 presidential election.

Five people, including Tapie, have been charged with conspiracy to commit fraud and IMF chief Christine Lagarde, who was finance minister at the time, and Claude Gueant, Sarkozy’s former right-hand man, have both been questioned in the case.

Some of Sarkozy’s supporters have lashed out against what they view as an unnecessary and humiliating detention of a former president; the Socialist government has been accused of pursuing the case to thwart Sarkozy’s political return.

Alain Juppe, a former prime minister from Sarkozy’s Union for a Popular Movement party, posted support on Twitter for the embattled ex-president: “His defence will show he is innocent, I hope.”

—Compiled from agencies