Mission that resulted in headless body of Buster Crabb washing up in harbour led to criticisms of intelligence service that remain topical, newly released files show

A disastrous MI6 operation that resulted in the headless body of a navy frogman being washed up in Chichester harbour provoked a furious row over who should be responsible for Britain’s secret intelligence service, hitherto classified files show.

Commander Lionel “Buster” Crabb was asked by MI6 to inspect the propeller and hull of a new Soviet cruiser, the Ordzhonikidze, which was moored at Portsmouth during Nikita Khrushchev and Marshal Nikolai Bulganin’s official visit to Britain in 1956. But Crabb vanished, and a coroner later ruled that a headless body found in June 1957 was his.

The operation had gone ahead “against my orders”, noted an angry Anthony Eden, the prime minister, papers show. MI6 claimed that the Foreign Office was informed beforehand, but it denied this. The head of MI6, Sir John Sinclair, resigned and was replaced by Sir Dick White, the head of MI5.

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An official inquiry attacked MI6 for “errors in tradecraft”, describing as “criminal folly” the decision by Bernard Smith, the officer in charge of the operation, to sign his real name and address in the register of the Sally Port hotel, where he stayed the night with Crabb before the operation. It also noted that the 47-year-old Crabb had not done any diving for six months. An inquest jury on Crabb recorded an open verdict.

The files released on Friday refer to a document setting out MI6’s responsibilities. It said: “Delicate operations are those which come into the category liable to produce the most serious embarrassment if they misfire, that is to say, they could be readily traced directly to British official action.” The message was that the Foreign Office, and by implication the foreign secretary himself, would have to authorise such operations.

The question of who is responsible for the security services remains topical. The authorisation of an MI6 rendition operation in 2004 involving the abduction of two prominent Libyan dissidents and their families, and their subsequent torture in Tripoli, is the subject of a current Metropolitan police and Crown Prosecution Service inquiry.

The newly released MI5 files also reveal that the Tory peer Robert Boothby and East End gangster Ronnie Kray went to “homosexual parties” together and were described as “hunters” of young men. Boothby denied having a relationship with Kray, but the files suggest he was much closer to him and his brother Reggie than he admitted.

Roger Hollis, then head of MI5, noted that the home secretary and some of his colleagues felt that it “might develop along the lines of the Profumo affair”. But Hollis said he felt “no security issue was involved”, as Boothby – a long-term lover of Dorothy Macmillan, wife of the former prime minister – had no access to official secrets.