In his last investigation before he was murdered, Alexander Litvinenko claimed to have uncovered a plan by the Russian Federal Security Service to claw back millions of pounds from wealthy Russians who fled to London and other Western capitals.

Most of the exiled executives are said to have worked for Yukos, the $10 billion energy giant seized by the Kremlin. Litvinenko had visited some of the alleged targets to warn them that the Russian intelligence services planned to intimidate them and their families to recover millions of dollars.

He also claimed to have discovered the amount of money that those on the list were expected to hand over, and that teams of Russian agents were being sent abroad to track them down.

Most of those on the list already knew the danger they faced: a number of former Yukos officials have been murdered or jailed or have disappeared in recent years.

Stephen Curtis, the British managing director of a company that had been the main shareholder in Yukos, died in a helicopter crash close to his palatial home in Dorset in March 2004. He died a fortnight after he went to Scotland Yard saying that he had received death threats. He told detectives that he feared that a hit team had been sent from Moscow to assassinate him.

Yuri Chaika, the Russian prosecutor-general, who has taken over the investigation into the Litvinenko affair, has been conducting a fresh inquiry in Moscow into the Yukos affair. Official approaches that President Putin has made in the past three years to Whitehall and other Western governments has, however, failed to persaude them to send back a single person on the Kremlin’s wanted list.

Mr Chaika announced this week that he was extending his Yukos investigation until March, although Russian officials do not expect governments such as Britain to change their minds. Mr Chaika might now use the Litvinenko affair as an excuse to send prosecutors to London to seek access to exiled Russian millionaires.

At least a dozen former Yukos personnel have been given asylum in Britain, including a former vice-president, Alexander Temerko, and senior figures such as Dmitry Maruyev and Natalia Chernyshova, whom the Russians have charged with fraud. All deny any wrongdoing. Three attempts by the authorities in Moscow to have the 12 sent back to Russia were blocked by the English courts.

Litvinenko claimed in his dossier that the FSB decided to take matters into its own hands to recover billions of dollars through a covert campaign of intimidation, dirty tricks and murder. He flew to Israel in secret weeks before he was murdered to meet Leonid Nevzlin, one of the most wanted of the targets.

Mr Nevzlin was second in command at Yukos and the business partner of Mikhail Khodorkovsky, who is in a Siberian jail sentenced to nine years for fraud. Litvinenko was too scared to write down all his information and insisted on telling Mr Nevzlin and others in person about FSB plans for them. Mr Nevzlin said that the Litvinenko investigation “shed light on most significant aspects of the Yukos affair”. He has now passed the dossier to Scotland Yard, believing that Litvinenko’s delving into the Yukos connection was a reason his enemies at the Kremlin wanted him silenced.

Detectives investigating his poisoning last week questioned as a witness another former KGB officer, Yuri Shvets, who knew Litvinenko and was aware of his dealings with Yukos. There are some who have questioned Litvinenko’s motive for getting involved in the Yukos affair. Friends such as Alex Goldfarb said that the former KGB spy, who was given British citizenship last month, wanted to illustrate how the Kremlin was sending hit teams abroad to deal with its enemies.

A London-based academic, Julia Svetlichnaja, claims that Litivineko confided in her that his plan was to blackmail some of those on the FSB target list. Ms Svetlichnaja, 33, who is writing a book on the Chechen conflict, said that she received more than 100 e-mails from the dissident.

Litvinenko knew Curtis, whose job it was to set up this impenetrable network of accounts for Yukos executives that stretched from Mauritius to the Dutch Antilles.An the inquest into his death, his wife said Mr Curtis had received threatening letters and had told relatives that if anything “untoward” happened to him “it will not be an accident”. The jury ruled that the crash was an accident.

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