Government ministers feared the body of a Royal Navy diver who vanished while spying on a Russian warship for MI6 could have been captured and used for propaganda, official documents reveal.

Lionel ''Buster'' Crabb disappeared on April 19 1956 as he carried out surveillance in Portsmouth harbour on the Ordzhonikidze, a cruiser that had brought Soviet leaders Nikita Khrushchev and Nikolai Bulganin to the UK on a diplomatic visit.

The mishap left security chiefs, senior civil servants and top ministers scrambling to cover up an operation that was bungled so badly it bordered on ''criminal folly''.

An inquiry found that Bernard Smith, the MI6 agent handling Commander Crabb, had booked them into a hotel using their real names and addresses in the register, sparking fears they could be traced.

When local police were asked for advice on what to do about the register, a senior officer took matters into his own hands and made the ''regrettable'' decision to rip out the relevant pages, fuelling interest in the case from the press.

And it emerged that people outside the operation knew Cdr Crabb was diving in Portsmouth, including his business partner in a furniture company who told officials he was so worried about the disappearance he was planning on consulting a clairvoyant, Madame Theodosia.

Officials desperately tried to hide the failed mission from the press and ministers, deciding to pin the blame on the Admiralty. But after senior staff got involved the issue was eventually brought to the attention of the prime minister, Anthony Eden.

Mr Eden had previously banned a similar operation and was fuming that although he ''had made it clear that adventures of a similar nature were forbidden'', his orders were ignored.

The previously unseen government papers, released by the National Archives at Kew, west London, also revealed deep concern that an inquest into Cdr Crabb's apparent death could cause huge public embarrassment.

Officials felt it most likely that his body was still in the water after being killed by Russian counter-measures and there were fears that ''if it was aboard the Russian ship, they might produce it for propaganda purposes at an opportune moment either dead or alive, or they might dispose of it after leaving Portsmouth''.

Later, after the Russian delegation had left the UK without an international scandal rearing up - despite a Russian admiral telling his British counterpart they had spotted a frogman by the ship on the day in question - it was agreed that Cdr Crabb's friends and family should be informed that ''he had disappeared while on some secret Admiralty work''.

Ministers and officials debated the dilemmas of publicity that an inquest might bring, if one was ordered, though the Home Office felt it could persuade a coroner to ''avoid awkward questions'', but it was agreed to issue a certificate of presumption of death from the Admiralty, which ''would involve much less publicity even if it is irregular''.

But the failed operation was so grave that the heads of MI5 and MI6, as well as senior naval and Foreign Office staff, were summoned to give evidence to an inquiry led by Secretary to the Treasury Sir Edward Bridges.

It emerged the operation was sanctioned only because of misunderstandings between the Foreign Office and a senior MI6 officer.

''C'', the chief of MI6, said that despite being advised that the operation was ''highly secret, delicate and must be unattributable'', Mr Smith had ''neglected certain basic principles of tradecraft which ... should have been second nature to him''.

His signing of real names and addresses was ''criminal folly'', Cdr Crabb should have been watched more closely and a cover plan should have been prepared.

A memo revealed that Bridges ''was satisfied that the Crabb operation was a thoroughly bad and unplanned one''.

''No serious steps seemed to have been taken to conceal the movements of the participants or to plan any cover story,'' it said.