A CORPORATE bribery trial billed as the biggest in history opened today against oil giants Shell and Eni over an £800 million scandal to win control of a lucrative oilfield in Nigeria.

The firms’ size makes it the biggest trial ever and it is unprecedented that Eni’s current chief executive Claudio Descalzi remains in his post while he faces such serious charges.

“We have never seen a sitting CEO of an oil major go on trial for bribery,” said Barnaby Pace, a campaigner with activist group Global Witness.

The trial was later postponed until May 14 for technical reasons. The Nigerian government and four non-governmental organisations, including Global Witness, submitted requests to be considered damaged parties and allowed to participate.

The groups all worked together to get documents to prosecutors in Milan, as well as in other jurisdictions, that helped bring to the Nigerian case to trial.

Mr Descalzi is one of 13 individuals charged in the case involving the 2011 purchase of the OPL245 block. Other defendants include his predecessor Paolo Scaroni, two former top Shell executives, a former Nigerian oil minister, and a series of middlemen and advisers. The companies themselves are also corporate defendants.

Prosecutors allege that £375m of the £800m paid into an escrow account was converted into cash and distributed as bribes, while several hundred million more went to a former oil minister.

Since the charges were filed, prosecutors also have opened a separate investigation into allegations that Eni lawyers tried to throw investigators off of the Nigeria case. Authorities searched their offices in early February.

Shell and Eni, which is 30 per cent owned by the Italian government, both deny the allegations.