A whistleblowing Russian businessman who lived in Weybridge was on an assassin’s hit list and possessed "explosive" secret documents, a coroner’s court has heard.

Alexander Perepilichnyy, 44, was found seriously ill in the exclusive St George’s Hill estate on November 10, 2012, and died shortly afterwards.

His death was originally thought to be non-suspicious after two post-mortem examinations, but an inquest was called to investigate.

Earlier this year it was revealed a Chinese plant toxin, gelsemium, had been found in his stomach and a four-day inquest was adjourned to allow Surrey Police to investigate.

Mr Perepilichnyy had moved to Britain three years earlier, after an alleged falling out with a Moscow crime syndicate.

It emerged he was helping Swiss authorities in a major corruption investigation involving a multi-million-dollar fraud. He had been publicly named as the source who led to the Swiss criminal proceedings.

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

At a coroner’s hearing in Woking today Henrietta Hill QC, representing investment fund Hermitage Capital Management, said Mr Perepilichnyy told Hermitage he had received death threats and had taken out life insurance.

She said: "The deceased learned that during the arrest of organised criminals, described as professional assassins, his name was on a hit list.

"This is a man who on his own evidence was a marked man.

"The information and documents received from Mr Perepilichnyy was explosive.

"There must be some concerns about the initial steps of the police in their investigations."

She said the presence of toxin in his body was "of the gravest concern".

But the court heard an expert tasked with confirming the presence of gelsemium has not found time to do so since the last hearing in May.

The businessman had had a number of meetings with Hermitage during which he provided information that prompted the Swiss investigation.

The last meeting took place just five days before his death, Miss Hill said.

Making reference to the death of Alexander Litvinenko, she added: "[There is] concern that this is part of a pattern of reprisal killings."

Asking to be considered an interested party in the inquest, she said: "My client had a significant amount of contact with the deceased leading up to his death," and suggested that contact may had have had a direct link to that death.

Alexandra Tampakopoulos, representing Mr Perepilichnyy's family, said: "There is no direct evidence to support the connection that Mr Perepilichnyy was murdered.

"Positive evidence has been put forward by the family that supports death by natural causes."

He was not afraid but had received threats, she said.

She added: "If he was in fear of his life one would think he would not go jogging alone on the day that he was killed."

"Mrs Perepilichnyy does not want her husband's death to be used by others to further their agenda."