Former French President Nicolas Sarkozy on Tuesday denied being responsible for massive overspending on his failed 2012 re-election bid, in a second court appearance this year after his March conviction for corruption.

The 66-year-old right winger is on trial in Paris for illegal campaign financing -- one of several cases stemming from a flurry of investigations into his affairs since he lost his presidential immunity.

In March, he became France's first post-war president to be given a custodial sentence when judges handed him a three-year term, two years of which were suspended, for corruption and influence peddling over attempts to secure favours from a judge.

Sarkozy has appealed against that conviction.

On Tuesday, he made his first appearance at the second trial, which relates to the millions of euros in overspending on his attempt to win a second term in 2012.

Prosecutors say accountants had warned Sarkozy he was set to blow past the official 22.5 million euro ($27 million) spending cap. But he insisted on holding more events to fend off Socialist rival Francois Hollande.

Sarkozy told the court on Tuesday he had been too busy running the country to pay attention to "an accounting detail".

Denying allegations of runaway spending as a "fairytale" he said that a friend of his singer wife, Carla Bruni, had composed the music for one of his biggest rallies for free.

"I spent 40 years in politics, it's my life, I know how campaigns work," he told the court, insisting. "Things did not get out of hand."

In the end, his campaign spending came to at least 42.8 million euros.

His Union for a Popular Movement party, since renamed the Republicans, picked up most of the tab.

Sarkozy and 13 others are accused of setting up or benefiting from a fake billing scheme to hide the excess spending.

Unlike some of the defendants, Sarkozy has not been charged with fraud and claims he was unaware of the scheme. He faces the lesser offence of illegal campaign financing.

Sarkozy was in court for the second time this year
Sarkozy was in court for the second time this year AFP / Christophe ARCHAMBAULT

If convicted, he risks up to a year in prison and a fine of 3,750 euros.

The trial is set to run until June 22.

The case is known as the Bygmalion affair, after the name of the public relations firm hired to orchestrate a blitz of lavish US-style election rallies.

Bygmalion executives have admitted to using a system of fake invoices to mask the real cost of the events.

The investigation failed to prove that Sarkozy had any hand in the fraud but the prosecution argues that it was his choice to hold the "elaborate, extravagant rallies" that blew the budget.

Sarkozy said Tuesday that the only instructions he gave his team was to order high-quality sound and lighting systems.

"I didn't want to ruin my voice, I'm not (pop singer) Patrick Bruel," he said, adding that he was also anxious to avoid looking "pasty" on television.

In March, Sarkozy was convicted of corruption and influence peddling after being found guilty of plotting with his lawyer to obtain confidential information from a judge about an inquiry into his 2007 election campaign.

Even if he loses his appeal he is unlikely to spend time behind bars, with the court ruling he could serve his year-long term at home, wearing an electronic bracelet.

The conviction dealt a blow to the hopes of his supporters that he could stage another comeback.

In a television interview on March 3, he repeated that he had "turned the page" on his political career but made clear he would continue to anoint right-wing favourites.

Sarkozy is married to singer and former model Bruni, with whom he has a nine-year-old daughter.

He has also been charged over allegations that he received millions of euros for his 2007 election campaign from the late Libyan dictator Moamer Kadhafi.

And in January, prosecutors opened a probe into alleged influence-peddling involving his activities as a consultant in Russia.