Virendra Rastogi (39), Anand Jain (43) and Gautam Majumdar (57), ex-directors of metal trading business RBG Resources, were convicted at London's Southwark Crown Court of conspiracy to defraud on 23 April.

Pronouncing the sentence yesterday, Judge James Wadsworth said: "They created a very impressive front that fooled banks, the metal exchanges in both countries, (UK and USA), and well respected accountancy firms".

"They were involved in years of calculated dishonesty." During the trial, he noted that "they had shown no shadow of regret or remorse or repentance."

Rastogi, who has earlier figured in the Sunday Times Rich List, was sentenced for nine years and six months, Jain for eight years and six months and Majumdar for seven years and six months.

In addition, the three have also been disqualified from acting as company directors for various periods: Rastogi for 15 years, Jain for ten years and Majumdar for ten years.

The sentences came at the end of a long drawn out international investigation. When investigators from the Serious Fraud Office swooped on Rastogi in his Mayfair apartment here in 2002, he was found shredding wads of documents.

For six years, Rastogi reportedly conned banks into funding non-existent metal trading deals using 324 fake companies that turned out to be based in small flats and shops, with few assets beyond a table and chair.

The address of one company turned out to be a cowshed in India and another was a launderette in America. Hundreds of millions of dollars and pounds circulated around the globe on the instruction of the conspirators.

This was a sophisticated and complex enterprise; it continued for over four years, in increasing amounts and fooled not only the banks (who undertook their own due diligence) but also the auditors," the SFO said after they were convicted.

It was an audacious fraud, underpinned by a very small amount of genuine business, which could be used to give credence to the wider claims of the businesses, the SFO added.

RBG went in to liquidation in 2002, but in the years before its collapse, it was presented to its bankers, auditors and regulatory exchanges as an aggressively developing and successful business.

"The truth was in stark contrast to this impression. Banks in the UK and elsewhere were persuaded to provide extensive financial facilities to RBG effectively secured against debts due to RBG from sales to customers," the SFO said.

In the event these debts proved valueless as the transactions were not, as the banks believed, with independent third party customers but with companies, controlled by the Rastogi family around the world, it said.

The fraud was discovered during investigations by the liquidators and the SFO, which also involved the Southern District of New York US Attorney's Office and FBI in the USA as well as Department of Justice and Police in Hong Kong.