It is a story with a plot that has all the elements of a Graham Greene novel: murder, sex and the murky world of international diplomacy. At its centre is an unlikely protagonist, Craig Murray, our man in Tashkent.

Earlier this month, the ambassador to Uzbekistan was suspended by the Foreign Office for speaking out against human rights abuses in the former Soviet republic. These include political dissidents being boiled alive and the use by MI6 of “intelligence” extracted through torture in Uzbek jails. The Scots diplomat’s supporters have cast him as a victim of conscience who has risked everything to stand up for his principles and expose Britain’s supposed ethical foreign policy as a sham. Murray’s detractors have dismissed him as a loose cannon whose sanity and motivation ought to be questioned.

However, a new explanation has emerged, which may explain his determination to break with diplomatic protocol and speak his mind. Murray says he has a serious medical condition and expects to be dead within five years. Because of his affliction, the 45-year-old, who spent his childhood in South Queensferry, feels he has nothing to lose and intends to go down guns blazing, taking with him his former colleagues at the Foreign Office and Jack Straw, the foreign secretary.

Murray has enlisted the help of Gareth Peirce, the leading human rights lawyer, who has represented the Birmingham Six and Guildford Four, to sue the Foreign Office for damages over false allegations that he demanded sex for visas, drank to excess and drove an embassy car down a flight of steps.

According to friends, Murray will claim that the charges were an attempt to smear his reputation and force him out of his job. Furthermore, he will argue that the “vexatious” allegations, caused the incurable heart condition.

“I have pulmonary hypertension, a condition which requires an excessive amount of pressure to force blood through the lungs, which has led to a 20% enlargement of the valve on the top right heart valve,” he says. “Last November I developed pulmonary emboli which almost killed me. They were caused by stress and have, in turn, caused the hypertension.

“I could be here in 20 years’ time but nobody is going to bet on it.”

His friends are less sanguine. “He knows he may have only three to five years to live and this has made him determined to get to the bottom of what went on behind the scenes as soon as possible,” says one.

“The Foreign Office brought vexatious disciplinary charges against Craig, which were exaggerated beyond all measure. Stress levels were upped in order to force Craig to resign and have caused significant damage to his health. All this was done in order to silence his views on human rights and the use of torture to obtain intelligence.”

It is also understood that Murray plans to force the foreign secretary into the witness box, to explain his involvement and that of the American government.

Friends claim the diplomat believes Straw may have been responsible for forcing him out of his job, following pressure from Washington. America has oil interests in Uzbekistan and is said to have turned a blind eye to abuses of religious and political dissidents by the Uzbek government in return for its support in the war on terror and the use of an airbase in the country that is crucial for military operations in neighbouring Afghanistan.

“He has been told by sources within the Foreign Office that pressure was brought by the Americans on No 10. If there was American involvement then Craig wants to find out what was discussed with the American government and the Uzbek government,” says the friend.

Aside from the impact on his health, events in Uzbekistan also led to the collapse of his marriage. Earlier this year he admitted to having an affair with Nadira Alieva, a 22-year-old Uzbek hairdresser. Fiona, his wife of 20 years, left him and returned to Britain with their children, Jamie, 15, and Emily, 9.

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