MI6 is one of Britain’s most elusive organisations. Its head, Richard Dearlove, is virtually unknown – a contemporary photograph has never appeared in the press. Britain’s Secret Intelligence Service clamps down on any dissident reports of its activities and despite the architectural prominence of its London headquarters at Vauxhall Cross, its operations and structures remain veiled from scrutiny. Even its true budget is a secret.

To write about MI6 risks harassment and prosecution, as former members and current commentators know to their cost. It is impossible, under the laws presently shielding MI6 and its sister service, MI5, to write about its daily activities: there is no right to know what is undertaken abroad today in the name of Britain’s security. But MI6 has a history, and that reveals a great deal.

Stephen Dorril is a meticulous observer and chronicler of the security services, and in this portrait he offers the fullest possible vision of MI6’s motives, character and, crucially, what it has done and where it has been most influential. At the beginning of the Cold War, Britain was a global power literally dividing up the world. By 1992 influence abroad had been lost in the Middle East, most of Africa and large swathes of Asia, and even in Europe Britain seemed exiled and isolated. What had MI6 been doing? MI6’s post-war activities were grounded in pre-war attitudes and practices, at home in the clubs of Pall Mall and St James but little suited to a retreating post-imperial power. Britain’s management of the Cold War was in the itching hands of a mixture of frustrated former members of the wartime SOE, desperate for active military engagements, anxious reactionaries who saw more to fear from Clement Attlee’s Labour Party than from any red menace abroad, and a few socialist devotees for whom communism was the future and spying the career of choice.

Here for the first time is an operational history of MI6’s activities and attitudes in action. It is at times stirring, at other times full of bathos or low farce. Symbolic of the entire period is the lengthy and expensive operation to dig a tunnel under East Berlin to intercept Soviet information. The tunnel took years to dig, and was known to the East Germans before it became operational. When it finally went live it intercepted such a vast amount of data that it took decoders in the UK three years to sift through all the information – by which time those items that were not faked were out of date.

MI6 is a vital, essential arm of the state. It is Britain’s player at the chessboard of international intelligence-gathering. Dorril’s is a searching story of the characters and situations in which the games have been played, from the back streets of Aden to the Brandenburg Gate, the mountains of Albania to the shores of the Black Sea. This is a discreet history of half a century of international political intriguing, spying and thuggery – all in the name of intelligence.

Stephen Dorril has worked on ‘Lobster’, the journal devoted to the activities of the intelligence agencies. He is the author of ‘Smear’ and a book about MI5, ‘The Silent Conspiracy’, and with Anthony Summers, ‘Honey Trap’, about the Profumo affair.