A Russian millionaire who died in mysterious circumstances after informing on corrupt Kremlin officials was not murdered, an inquest has concluded.

Alexander Perepilichnyy died of sudden arrhythmic death syndrome, coroner Nicholas Hilliard QC said. Campaigners said police “incompetence” had hampered the investigation.

The 44-year-old collapsed while jogging near his home in Weybridge, Surrey, in 2012, but because police did not immediately treat his death as suspicious, “significant” forensic opportunities were lost.

He was one of 14 Russians whose deaths in the UK were reviewed by the home secretary following the Salisbury poisonings.

Anti-corruption campaigner Bill Browder said the coroner was “working with a puzzle with only 20 per cent of the pieces”, blaming the “incompetence” of Surrey Police.

Mr Browder said: “I do not know how he was murdered, there’s no way we can without a proper investigation.” He said would not give up and would “work on this politically”.

Detective chief superintendent John Boshier, of Surrey Police, said the force accepted there were “organisational failings in the early stages” but found no evidence of foul play.

Mr Perepilichnyy, whose death was first reported by The Independent, was last seen running up a steep hill by a driver who described him looking pale and unwell, with his arm across his stomach.

Judge Hilliard said his illness “must have come on shortly” as he did not use his telephone to call for help.

He added: “Descriptions of vomit (near Mr Perepilichnyy) could not sensibly be viewed as evidence of poisoning and nobody who came into contact with him came into any harm.

“There is no direct or incontrovertible evidence that he was murdered at all.”

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Judge Hilliard examined whether the married businessman could have been poisoned after exposing a Russian money laundering operation and causing accounts to be frozen.

Delivering his findings on Wednesday, the coroner warned: “When it comes to human affairs, there will always be some matters that remain unresolved.”

He told the Old Bailey he was “acutely aware” of the distress caused to Mr Perepilichnyy’s widow and family by the inquest proceedings and the length of time it has taken to reach a conclusion.

Police said they found no evidence of foul play at the time but were heavily criticised for the way they handled the investigation.

Crime scene investigators did not attend the incident as the death was not immediately ruled suspicious, which meant photographs, CCTV footage and other potential evidence was not gathered.

A forensic post-mortem examination was not carried out for 18 days, which Judge Hilliard called a “significant lost opportunity”, and the contents of Mr Perepilichnyy’s stomach were thrown away.

Police did not examine two phones recovered from his body and it also emerged that data on his computer had been lost.

Hearings held earlier this year were told that Mr Perepilichnyy had been blowing the whistle on alleged organised crime in Russia.

He had been helping Mr Browder’s Hermitage Capital Investment expose a $230m (£142m in November 2012) money-laundering operation, the inquest was told.

Mr Perepilichnyy was helping Swiss prosecutors investigate corrupt Russian tax officials who were allegedly involved in the scheme and became a key witness against the “Klyuev” group.

Hermitage had previously hired Russian lawyer Sergei Magnitsky to investigate the scam and he publicly named a number of key interior ministry officials as involved, but was arrested and died in custody in November 2009.

The George V hotel in Paris where Mr Perepilichnyy stayed before his death (AFP/Getty)

The Klyuev group, a shadowy network of corrupt Russian officials and underworld figures, were implicated in his death as well as a series of multimillion pound tax frauds.

Russia’s interior ministry claimed the complex scam against Hermitage was carried out by a sawmill worker and a convicted burglar, who were jailed. They were said to have been in cahoots with three others who have since died.

Mr Perepilichnyy died before he could give evidence against his former private banking clients.

After his death, Mr Browder said Hermitage wrote to police urging them to investigate it as potential murder and “act as quickly as possible to secure the evidence and look for toxicology tests”, but did not get a response.

Mr Hilliard said those behind the fraud on Hermitage had an obvious motive to stop Mr Perepilichnyy from giving evidence against them at an upcoming hearing in Switzerland.

But he noted that Mr Perepilichnyy was not a high-profile critic of the Kremlin, unlike others who were previously murdered.

The father-of-two was said to have appeared on a “hit list” in Moscow before his death and had taken out £3.5m of life insurance and applied for another £5m of policies.

Mr Hilliard said he “heard evidence Mr Perepilichnyy felt in fear for his life and safety”.

A month before his death, he had fought off a legal challenge by a debt recovery firm allegedly led by a prime suspect in the Alexander Litvinenko assassination, Dmitry Kovtun.

The night before his death, Mr Perepilichnyy had been sick after a meal out at a fish restaurant in Paris with his mistress Elmira Medynska, 28, the inquest heard.

She told the coroner that he had been feeling unwell after a meal and locked himself in a bathroom for an hour while vomiting.

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He returned to the UK the next day and appeared “completely normal” as his wife prepared one of his favourite meals for lunch, a traditional a sorrel soup, the inquest heard.

Mr Perepilichnyy then collapsed on his regular jog from their rented home in St George’s Hill in Weybridge, Surrey.

Extensive tests have failed to identify any poison in his body, although experts could not categorically rule out a toxin or even a nerve agent such as novichok.

It was alleged an undetectable poison could have been used, or that the opportunity to identify it was lost due to police failings.

Data lost from Mr Perepilichnyy’s computer included alleged evidence of half a billion dollar transactions, threats and links to the money laundering case, the inquest was told.

The coroner resisted calls for disclosure on whether Mr Perepilichnyy was in contact with British intelligence after a government application for secrecy in the national interest.

Judge Hilliard said he received a letter from counterterror police confirming they “are not conducting an investigation into Mr Perepilichnyy’s death” at the hands of a “hostile” agent.

“There is nothing that points significantly towards poisoning rather than sudden arrhythmic death syndrome,” he added.

Widow Tatiana Perepilichnaya had said the family moved to Britain from Moscow in 2009 for the sake of their children’s education and because she felt “at home in London”.

Judge Hilliard said that as a “very wealthy man”, Mr Perepilichnyy was the recipient of a “tier one” visa that had required an investment of at least £1m in Britain.