The euphemistic-sounding Operational and Technical Directorate succeeded Kamera (the Russian for chamber), the Cold War poison factory created by Stalin, but it still has a laboratory devoted to finding new ways of killing people.

It supplies the lethal products for Department 12 of Directorate S of the SVR (the Russian foreign intelligence service), which deals with biological warfare.

Oleg Kalugin, who spent 32 years in the KGB and now lives in the West, revealed in his exposé of Russian espionage, Spymaster, that the laboratory invented poisons that agents could slip into drinks, and jellies they could rub on a person to induce a heart attack.

He said that several options were discussed when plans were made to liquidate the Bulgarian dissident Georgi Markov in 1978: using poison jelly, poisoning his food or shooting him with a poison pellet. One plan was to rub poison jelly on to the handle of Markov’s car door, but this was rejected because the wrong person might have opened the door and Markov would have been warned off.

Then it was discovered that Markov was planning a holiday at a seaside resort in Italy and a plot was devised to bump into him and smear him with poison jelly on the beach. But that plan was also scrapped because the weather was cold and Markov never went swimming. So the KGB resorted to the third option: a ricin pellet shot into his leg while Markov was walking across Waterloo Bridge.

The history of Kamera, or Laboratory 12, is peppered with cases where the KGB has turned to the most mysterious and most undetectable poisons. Nikolai Khokhlov, a defector from the KGB, had radioactive thallium slipped into a cup of coffee while he was at a public reception in Germany in 1955. He survived.

Friends who had waited by Mr Litvinenko’s bedside feared that his attackers had developed a new drug to poison him. They said that experts had run through every toxin they knew of, but the doctors had never encountered such a case.

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