Doctors remained baffled last night over the mystery poison that struck down a former Russian prime minister a day after the former FSB agent Alexander Litvinenko died.

Yegor Gaidar remained in a Moscow hospital as tests continued to establish what caused him to collapse, vomiting blood, during a visit to Dublin. His daughter, Maria, said that he had been unconscious for three hours and close to death.

Irish officials said last night that tests at the Dublin hospital where Mr Gaidar was treated showed no trace of radiation.

Valeri Natarov, the spokesman for Mr Gaidar, told The Times that the politician had felt fine before his trip and had complained of feeling ill only once he was in Ireland. He said there was no doubt that Mr Gaidar had been poisoned.

Mr Natarov declined to comment on reports that security guards were protecting the 50-year-old politician at an undisclosed hospital. “I spoke with him briefly today and it is clear that his health is improving. Mr Gaidar has no big political enemies in Russia,” he said.

“He is an economist, he writes books. There needs to be a thorough investigation into the case once we have the results of the medical tests.”

Mr Gaidar was the architect of “shock therapy” reforms in the early 1990s that introduced a market economy after the collapse of the Soviet Union.

Many blamed him for plunging the country into poverty.He has been out of active politics for at least a decade.

Mr Gaidar visited Poland and the US shortly before flying to Ireland from Moscow to discuss his latest book at a conference last Friday. He spent the night at James Connolly Memorial Hospital in Dublin then returned to Moscow for further treatment.

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