A team of British detectives has flown to Bulgaria for the second time in three months to investigate the murder of Bulgarian dissident Georgi Markov after new information is said to have come to light.

Markov, who fled Communist Bulgaria in 1969 for Britain, where he worked as a journalist, was stabbed in the leg with an umbrella on Waterloo Bridge in London on September 7, 1978, while he stood in a bus queue.

He developed a fever and died a few days later in hospital without being questioned by police. A postmortem examination found a tiny ricin-filled metal pellet embedded in his calf.

When the Communist regime collapsed in Bulgaria a decade later a stock of assassination umbrellas was found at the Interior Ministry in Sofia.

Leading article: The murder of Mr Markov

He was killed by a tiny man-made metal object probably containing bacteria or a chemical poison

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Up to five officers from the Counter-Terrorism Command of Scotland Yard spent two weeks in Bulgaria last month, having visited the country only a few weeks earlier. It is understood that they were following up a specific line of investigation.

The team is said to have requested documents, Andrei Tsvetanov, the Bulgarian investigator in charge of the case, told a Bulgarian newspaper. They also asked for permission to question about 40 witnesses, including two former top-secret police officers.

“We are fully cooperating with our colleagues and are having a 100 per cent exchange of information on both sides - something we lacked in the past,” Mr Tsvetanov told Dnevnik.

A spokesman for Scotland Yard said that officers reviewed the case periodically. The investigation has been all but closed in Bulgaria because its 30-year statute of limitations expires in September.

In 1992 Oleg Kalugin, a former KGB counter-espionage chief, claimed that Todor Zhivkov, the Bulgarian communist dictator, had ordered the murder.

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