A long-awaited public inquiry into the death of Alexander Litvinenko began in London on Tuesday (January 27), just over eight years after the former KGB spy died after drinking tea poisoned with a rare radioactive isotope in the British capital.

From his deathbed, Kremlin-critic Litvinenko, who had been granted British citizenship, accused Russian President Vladimir Putin of ordering his murder and British authorities say there is evidence to charge two ex-KGB agents with murder.

Russia has always denied any involvement in his death, although Robert Owen, the judge who will act as the inquiry chairman, has said there is "prima facie" evidence of Russian culpability in the 2006 death.

"The issues to which his death gives rise are of the utmost gravity and have attracted worldwide interest and concern," said Owen in his opening statement.

British police believe Litvinenko was poisoned with tea laced with the rare isotope polonium-210 at the Pine Bar of the Millennium hotel in central London in November 2006 where he was meeting former Russian spies, Andrei Lugovoy and Dmitry Kovtun.

He died three weeks later.

Lawyer for the inquiry, Robert Tam detailed Litvinenko's life during his opening statement saying the family's flight from Russia "would not disgrace the pages of a thriller".

Tam also revealed that Litvinenko tried to protect Russian oligarch Boris Berezovsky who was living in London and helping him financially.

"There is evidence that in 1997 Mr Litvinenko's unit was given orders to kill Mr Berezovsky which Mr Litvinenko believed to be improper orders. Mr Litvinenko warned Mr Berezovsky and tried to report the matter to the senior leadership of the FSB. This included a meeting in July 1998 between Mr Litvinenko and the head of the FSB, who had then been newly appointed. Sir, that man was one Vladimir Putin," said Tam.

As ties improved, Britain rejected holding an inquiry in 2013, admitting the relationship with Russia was a factor although not a decisive one. However, with relations subsequently soured by the Ukraine crisis, the British government changed its mind and gave the go-ahead for the inquiry last July.

The public inquiry is expected to last around ten weeks.