The Foreign Office is threatening action against Craig Murray, the former ambassador to Uzbekistan, if he publishes an unauthorised book attacking the use of intelligence obtained under torture.
This comes after the blocking of key parts of an account of the Iraq war by another of Britain's senior diplomats, former UN ambassador Sir Jeremy Greenstock, in which he calls the US decision to invade "politically illegitimate".
Mr Murray has failed to submit his memoirs for clearance and the Foreign Office said yesterday there were a "range of options" open to it if he went ahead.
Although it would, in theory, be possible to prosecute him under the Official Secrets Act, the government is more likely to bring a civil action against him for breach of confidence.
Mr Murray was deprived of his ambassadorship last year after the leak of a report in which he criticised the use of torture material by MI6. He said yesterday: "I'm not surprised the government want to ban my book. It contains a lot of information they don't want to have known. None of it concerns national security, but illegal and underhand behaviour by the British government".
Mr Murray's friends say he is "unlikely" to comply with a demand that he submit the manuscript for approval.
Last year, after a failed attempt by the Foreign Office to sack Mr Murray for alleged disciplinary shortcomings, a report was leaked about a London interdepartmental meeting in July 2004 on the use of intelligence from Uzbekistan, where the president, Islam Karimov, has been accused of brutality against dissidents.
In the leaked document, Mr Murray, who stood as an independent election candidate against the foreign secretary, Jack Straw, said MI6 was taking information via the CIA obtained by torture.
"Tortured dupes are forced to sign confessions showing that the Uzbek government wants the US and UK to believe - that they and we are fighting the same war against terror. This is morally, legally and practically wrong."
His colleagues argued that they did not know for a fact whether informants had been tortured: "I will not attempt to hide my utter contempt for such casuistry, nor my shame that I work for an organisation where colleagues would resort to it to justify torture."
The former ambassador says he was not responsible for the leak which ultimately led to his removal. He has written to the Foreign Office in response to their demand that he submit his memoirs for censorship, saying he is taking legal action over his "appalling treatment".
The material in his book had already featured in a "host" of articles, he said: "So if you want to take action under the Official Secrets Act, I suggest you get on with it".