A MILLIONAIRE British lawyer killed in a mysterious helicopter crash is thought by US lawyers to have been the corporate mastermind behind one of the world’s biggest alleged tax evasion scandals.

Stephen Curtis is named in a lawsuit in America which has been brought by a group of investors who say they have lost up to $1 billion (£541 million) in the collapse of Yukos, the Russian oil giant.

Mr Curtis is accused in the lawsuit of having orchestrated numerous offshore companies allegedly used as part of a scheme of “tax fraud and money-laundering” at Yukos.

This legal action comes as aviation experts and close friends of Mr Curtis voiced new doubts about the cause of the air crash in March which happened just days after he offered to provide information to British Intelligence about suspected illicit Russian business activities in Britain.

He confided to a business colleague that he had received death threats and discovered his home telephone had been bugged.

The Russian Government has accused Yukos of evading between £2.7 billion to £5.2 billion of tax dating back to the 1990s. Mikhail Khodorkovsky, the company’s chief executive, was arrested last November and is in prison in Russia awaiting trial for tax evasion and fraud. His 44 per cent share in the company has been seized by the Russian authorities.

At about the same time doctors had told Mr Curtis, 45, who was suffering from a rare blood disorder, that he had only months to live. A close friend said: “Stephen did not want to spend the time he had left tied up in lawsuits.”

What frightened him were threats reportedly made against his daughter, Louise. Until now it was believed Mr Curtis was merely a “bagman” for Russian oligarchs by setting up anonymous companies in offshore tax havens and moving large amounts of money and other assets around the world, apparently to avoid paying taxes.

Now US lawyers, who have conducted extensive investigations into Mr Curtis’s business dealings in Britain, Russia, the Isle of Man and Gibraltar, allege he was a key figure behind a global web of money-laundering and tax evasion which has crippled Yukos.

“Stephen Curtis served as the ‘corporate mastermind’ for organising the myriad of offshore structures . . . which were used as part of the scheme of tax fraud and money-laundering described herein,” the lawsuit states.

Darren Robbins, one of the lawyers leading the case, which was brought on July 27 by Roxwell Holdings, a Bermuda-based investment firm, said he believes Mr Curtis was more than just a lawyer for hire. “The allegations are and will be further highlighted that he was at the core of this alleged wrongdoing,” Mr Robbins told The Times from his San Diego office.

The legal action seeks compensation from, among others, Yukos Oil, Gibraltar-based Menatep Ltd which allegedly had a controlling shareholding in Yukos, and Mr Khodorkovsky.

Investigators working for Mr Robbins, one of America’s leading class-action lawyers, are already in Britain, the Isle of Man, Gibraltar and Russia in the hope of uncovering the billions of dollars Mr Curtis is thought to have spirited away from Yukos.

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