London (CNN) -- Britain's government has evidence Russia was involved in the mysterious poisoning death of former KGB agent Alexander Litvinenko, who was at that time working for British and Spanish intelligence services, a lawyer has said. The allegation emerged at a hearing Thursday in London ahead of an inquest into Litvinenko's 2006 death that is due to start in May. In Britain, an inquest is an inquiry held where a death is sudden or unexplained to establish the facts around it. Read more: Russian magnate wins libel case over poisoning report Litvinenko, a fierce critic of Russian President Vladimir Putin, came to Britain in 2000 after turning whistle-blower on the FSB, the KGB's successor.
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Lawyer: UK government evidence suggests Russia tied to ex-KGB agent's death
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Alexander Litvinenko worked for MI6 and Spanish intelligence services, widow's lawyer says
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Litvinenko died after being poisoned by radioactive material polonium-210 in 2006
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Litvinenko on deathbed blamed Russia's Vladimir Putin, but the Kremlin denies the accusation
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The men were both to provide intelligence to the Spanish prosecutor investigating Russian mafia links to the @placeholder and to Putin, he said.