A former French energy boss now aged 99 stands trial Monday with others on charges of corruption, in a case dating back to 2002 that his lawyers slam as an abomination.

Jean Bonnefont is charged with distorting the energy market to ensure the favourable awarding of a contract for the heating and air conditioning of the La Defense business district in Paris.

Along with Bonnefont, a former executive of the Charbonnages de France mining firm, also going on trial at the court in Nanterre outside Paris are former Eaux-Vivendi executive Bernard Forterre, now 82, and businessman Antoine Benetti, 68.

"It is impossible to grasp that a 99-year-old man is going on trial," said Olivier Baratelli, Bonnefont's lawyer.

"Are you able to remember what you did twenty years ago with sufficient precision for it to be the subject of a trial?" he asked.

The defence lawyers will initially argue that the rights of their clients to the trial within a reasonable time has been violated.

Bonnefont is accused of ensuring the awarding of a contract to a group called Enertherm which had the same shareholder structure as the previous holder of the contract Climadef, a subsidiary of Charbonnages de France.

The offences are alleged to have taken place from 1999-2003, with the first case opened back in June 2002.

"The length of this procedure has been in the interest of no-one," acknowledged Nanterre prosecutor Catherine Denis, adding the time needed for such a complex case is revealing of the "insufficient means given for economic and financial justice."

All those on trial deny the charges. They face up to 10 years in prison if found guilty. 

The trial is due to last until Friday.