A court in London has ruled that the former vice-president of oil giant Yukos cannot be extradited to Russia.
Yukos came under investigation by Russian tax officials in 2003
Russian prosecutors had accused Aleksander Temerko, a close associate of jailed tycoon Mikhail Khodorkovsky, of defrauding a state oil company.
But the British judge concluded that Russian authorities wanted to punish him for his political opinions.
He said it was highly unlikely, if not impossible, for Mr Temerko to receive a fair trial in Russia.
Mr Temerko will now be allowed to stay in Britain, pending a possible appeal by the Russian authorities.
Mr Temerko became vice-president of Yukos in 2003, after the arrest of Mr Khodorkovsky, who is now serving a prison sentence in Siberia.
Mr Temerko says he believes the motivation of the assault on Yukos was President Vladimir Putin's desire to silence those who challenged him politically.
A number of internationally-respected specialists on Russian affairs spoke at Mr Temerko's hearings, describing why they considered the whole Yukos affair to have been politically motivated.
His lawyers were especially scathing over the performance of the Russian legal authorities. They said they appeared not to take the matter seriously, and had failed to produce any witnesses to back their extradition request.
Mr Temerko's representatives also stressed that a string of failed Russian extradition requests had cost British taxpayers millions of dollars in lawyers' and court fees.
While there was no immediate reaction from Moscow, legal counsel for Russia in London said it would consider appealing against the court's decision.
Previous rejections of extradition requests have led to angry outbursts of anti-Western sentiment in Russia, as well as accusations of unfairness and double standards in judging Russian cases.