To poisoning as assassination method

approval of Russian president Vladimir Putin. Russian expat Mr Perepilichnyy, 44, had eaten his favourite sorrel soup prepared by his wife before he collapsed while out jogging near his home in Weybridge, Surrey, in November 2012.

An inquest into his death heard an experienced assassin could have poisoned the Russian whistleblower, even though extensive tests failed to identify the toxin.

Bill Browder, the London-based human rights campaigner and professed “number one enemy” of Mr Putin, said Mr Perepilichnyy had told him he had been receiving death threats, “making it reasonably likely that a Russian assassin was on the loose in the UK”.

At the Old Bailey inquest, forensic toxicology specialist Dr Fiona Perry was asked if specially made rare poisons could be designed as a “warfare agent”.

She said it depended on what access people had to them, adding that it may be easy for them if, for example, they had a plant growing in their garden.

Peter Skelton QC, counsel for the coroner, suggested some poisons were “impossible to detect” and could be deployed by an “experienced assassin”.

In September 1978, Bulgarian dissident Georgi Markov was assassinated in London usingapoison-loadedumbrella.

The murder involved a minuscule dose of ricin, a toxin produced naturally by the castor bean plant.

KGB agents and senior members of Bulgaria’s secret police were suspected of being involved.