A Russian whistleblower thought to have been assassinated in Weybridge may have been poisoned by a vegetable toxin in his soup, an inquest has heard.

Alexander Perepilichnyy, 44, died after collapsing outside his home in St George's Hill following an afternoon jog on November 10, 2012.

His death sparked allegations of a “reprisal killing” after it emerged he had helped Swiss authorities in a major corruption investigation relating to an alleged multi-million-dollar fraud.

He was then publicly named as the source that led to the Swiss criminal proceedings.

Mr Perepilichnyy had fled to Britain three years before his death after an alleged falling out with a Moscow crime syndicate.

He had also testified against people linked to the 2009 death of anti-corruption lawyer Sergei Magnitsky, and was the fourth person linked to that case to have died in strange circumstances.

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Ravenscroft Road in the St George's Hill estate, where Alexander Perepilichnyy was found

At a pre-inquest review today at the Old Bailey, Bob Moxon-Brown QC, representing one of Mr Perepilichnyy's life insurers Legal and General, said a vegetable toxin may have been used to poison the Russian businessman.

The review heard that sorrel, an ingredient in a popular Russian soup, also bore the same atomic weight as Gelsemium Elegans, a Chinese plant toxin found in the contents of Mr Perepilichnyy's stomach at the time of his death.

Mr Moxon-Brown said: "It does seem very likely he was poisoned as to any other method. It does seem very likely that what we're talking about is a vegetable poison.

"The question of what Mr Perepilichnyy had for lunch is to be of some importance. No witness statement has been taken from his widow, who on the day he had lunch with.

"Currently at the moment, there was no intent from the coroner to call evidence on this."

Mr Moxon-Brown said it was "almost unbelievable" that Surrey Police, which has maintained Mr Perepilichnyy's death was not suspicious, failed to interview his widow after his death five years ago.

At previous pre-inquest reviews, it had emerged Mr Perepilichnyy had taken out “millions of pounds’ worth of life insurance” after receiving death threats, and was reportedly on a hit list.

Henrietta Hill QC, representing financial firm Hermitage Capital Management, had said at a pre-inquest review in March last year that the businessman had received threatening demands for a payment of €1 million in the months leading up to his death.

The case has also been dogged with numerous delays after an argument over whether documents, said to relate to the interests of national security, were to be publically revealed in the long-awaited inquest.

But a High Court order in November banned the disclosure of any of the materials being made public.

Mr Justice Cranston, sitting on the case, had said Surrey coroner Richard Travers, who had presided over the case for years, was now in an "untenable" position and did not have the security clearance to view the secret documents.

Recorder of London, Judge Nicholas Hilliard, was appointed to the role after Mr Travers stood down last year.

The full inquest is expected to take place from June 5 in London, and will last for three to four weeks.