New evidence has emerged of Britain's attempts to cover up the fate of a diver who vanished in 1956, while apparently spying on a Soviet warship.
Crabb "served his country honourably", his family say
Lionel "Buster" Crabb disappeared while spying on the Ordzhonikidze - which had brought the Soviet leader to Britain for talks - in Portsmouth Harbour.
Papers released at the National Archives set out his last known hours.
The Admiralty documents make clear that whoever sent him on his mission, it was not the Royal Navy.
The Russian ship had brought the Soviet leader Nikita Khrushchev for meetings with the British prime minister Anthony Eden and his ministers.
The newly-released documents show that an officer, who is still unidentified, took Crabb out in a small boat in Portsmouth Docks and stayed onboard as the diver disappeared below the surface.
The second time Crabb did not come back, and several months later a headless corpse, identified by a friend as Crabb, was found floating along the coast.
At the time Crabb went missing, the Navy tried to say he was feared drowned in Stokes Bay - another location altogether.
The incident wrecked attempts at a rapprochement between Britain and the post-Stalin government in Moscow.
The Russians protested they were being spied upon by their hosts and, in the Commons, the government was asked if the security services were out of control.
The papers make clear that the Royal Navy was embarrassed and appalled by the affair.
It was concerned the anonymous officer would have to tell a story at a subsequent inquest "inconsistent with the impression which we have tried to convey - that this was a naval operation".
A memo from Rear Admiral JGT Inglis, director of naval intelligence, on 21 June, explained that in a "bona fide" operation, there would have been "immediate and extensive rescue operations".
And the unnamed diving officer would have also taken action.
In fact, there was no rescue operation because "a search could not be carried out beside the Russian warships".
Adm Inglis pointed out that, instead, "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".
This could expose naval chiefs and the unidentified officer who accompanied Crabb, to charges of "negligence, lack of humanity and error of judgment", he feared.
The secret account of the anonymous officer who assisted Crabb on the day of his disappearance, was also made public for the first time.
He said he had been asked to assist him "entirely unofficially and in a strictly private capacity".
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."
Navy officials were keen for this officer not to appear in public at a subsequent inquest.
It was decided to dispatch a temporary clerical officer to represent the Admiralty instead.
One of the secret documents explained: "He knows nothing of the background to the story and will not be able to answer any embarrassing questions even if they are asked."
The same document said: "The coroner is aware of the background to the case and is not asking for the appearance of any embarrassing naval witnesses."
The coroner ruled that it was Crabb's body that had been found.
Freedom of Information
Howard Davies, archivist at the National Archives, said the extent of the cover-up suggested there was more about the case to be told.
And Crabb's family demanded the truth.
Lomond Handley, from Poole in Dorset, one of his few living relatives, said: "The people deserve to know what happened to a man who had served his country honourably and with integrity."
The latest revelations come just four months after BBC Radio Solent obtained a report into Crabb's mission with a Freedom of Information application.
The report showed that Crabb's intelligence service handlers did not take proper precautions to protect him or the secrecy of the mission.