The family of a Naval hero whose death was hushed up demanded yesterday to know the truth behind his mysterious disappearance.

Commander Lionel "Buster" Crabb, thought to have inspired Ian Fleming’s fictional superspy James Bond, went missing during a dive off Portsmouth in 1956.

Secret documents relating to the controversy were released to the public at the National Archives in Kew, south west London.

They reveal the determination of officials to cover up what really happened, even rejecting a request for maintenance from ex-wife Margaret Crabb.

Lomond Handley, from Poole in Dorset, is one of the few living relatives of Commander Crabb.

She said: "The people deserve to know what happened to a man who had served his country honourably and with integrity. He was a decorated war hero and a true patriot. I want the truth, the whole truth and nothing but the truth."

The Government was keen to play down embarrassing claims that Crabb had been spying on Russian ships docked in the harbour during the visit of Soviet leaders Nikita Khruschev and Marshal Nikolai Bulganin.

Prime Minister Sir Anthony Eden told the House of Commons that it would "not be in the public interest" to disclose the circumstances of his death. He added that "what was done was done without the authority or knowledge of Her Majesty’s ministers".

The cover-up prompted wild speculation for years, including claims that he was alive and well and living in Russia as an officer in the Red Navy, and others that he was killed by the Soviets.

The documents reveal that five months after Crabb’s death, WH Lewin, head of Naval Law, wrote in a memo: "If this came out ... it would not seem to square very well with our statement that Crabb had been out of the Navy for over a year at the time of his death."

The official Admiralty line following the incident on April 19 was that Crabb had been "specially employed in connexion with trials of certain underwater apparatus" and was missing, presumed drowned. But a memo from Rear Admiral JGT Inglis, director of naval intelligence, on June 21, explained that it was "considered essential" to avoid implicating top officers in Portsmouth.

In a "bona fide" operation there would have been "immediate and extensive rescue operations", he explained, while an unnamed diving officer who was with Crabb would have also taken action.

Instead, as Inglis points out: "The moment it became clear that a mishap had occurred (name blanked out) was ordered to return to his ship and take no further part in the affair."

If it had been a "bona fide" operation, this would have exposed the other officer and the CinC (Commander in Chief) to charges of "negligence, lack of humanity and error of judgment", which was considered unacceptable.

The secret account of an anonymous Lieutenant Commander, who assisted Crabb on the day of his disappearance, was seen publicly for the first time. He said he had been asked, as an expert diver, to assist him "entirely unofficially and in a strictly private capacity" and there is little detail in the story.

The officer said: "He carried sufficient oxygen for an absence of a maximum of two hours submerged. His actions until disappearance under the surface were normal, and the conditions for diving were good. He was not seen by me again."

Miss Handley said: "I find it astonishing that (there is) so much secrecy. This veil of secrecy is worse than sinister, it is bizarre. The authorities are not ready because certain papers have been kept back which should have been released by now."