It is 30 years since Bulgarian dissident Georgi Markov was assassinated in London using a poison-loaded umbrella � but the case may now never be solved.

It is 30 years since Bulgarian dissident Georgi Markov was assassinated in London using a poison-loaded umbrella - but the case may now never be solved.

The September 1978 murder gripped the world, fuelling Cold War paranoia with its combination of skulduggery and James Bond-style weaponry.

Although KGB agents and senior members of Bulgaria's secret police were suspected of involvement, the communist defector's killers have never been brought to justice.

Scotland Yard insists its investigation is ongoing, but under Bulgarian law the 30-year statute of limitation in the case is due to expire on Thursday, the anniversary of Markov's death.

It is feared this may mean that crucial evidence held in archives in Bulgaria could now be destroyed, ending hopes of proving who was responsible.

Conservative MP Julian Lewis has raised concerns in Parliament about the progress of the investigation on several occasions.

In March last year he tabled a Commons question asking what information the Home Office and police had about the whereabouts of Danish-Italian suspect Francesco Gullino, whom he described as "the alleged assassin of Georgi Markov".

Dr Lewis yesterday called on Sofia to give an "absolute guarantee" that the statute of limitations rule would not be used as an "excuse" to break off "what little co-operation they have been giving to Scotland Yard".

He said: "It really would be absolutely outrageous conduct if the Bulgarian government allowed the investigation to cease and the remaining evidence to be destroyed or handed back to the Bulgarian secret services, who have singularly failed to show any significant support for clearing up this dreadful crime."

Markov, a playwright and satirist who had broadcast scathing accounts of communist high life to Bulgaria, was the subject of two failed assassination attempts before he was finally killed.

The 49-year-old dissident was waiting at a bus stop in London on September 7, 1978.when he felt a sharp jab in his thigh and saw a man picking up an umbrella. A postmortem found he had been killed by a tiny pellet containing a 0.2mg dose of ricin.