Oct. 5 (Bloomberg) -- MI5, Britain’s domestic security agency, gave up some of its secrets with the publication of an authorized history by academic Christopher Andrew.

“The Defence of the Realm,” which is 1,032 pages long and published by Allen Lane, an imprint Pearson Plc’s Penguin Books unit, is the result of the Cambridge University historian’s review of 400,000 files over seven years.

“Almost every day I said to myself, ‘Crikey, I didn’t know that,’” Andrew told reporters at a news conference in London today. Seated next to him was Stephen Lander, a retired MI5 director-general.

The book tracks MI5’s beginnings as a two-man operation in 1909, its activities during the two world wars, the Cold War and against terrorists ranging from the Irish Republican Army to Islamic extremists who bombed the London Underground in 2005.

Andrew describes how the agency opened a file on Harold Wilson at the time of the Labour Party politician’s election to Parliament in 1945 and tracked his official contacts with the Soviets as a member of the British government.

The file was kept under the pseudonym of Norman John Worthington, “because of its unusual sensitivity,” according to the book. Wilson, who was prime minister from 1964 to 1970 and again from 1974 to 1976, suspected a plot by the security services to undermine his government. Andrew backed the MI5 view that no such plot existed.

In 1961, then-Labour Party officials including leader Hugh Gaitskell drew up a list of 16 Labour members of Parliament they believed to be members of the Communist Party and passed it to the security service, Andrew said.

‘Hard Target’

Andrew, who is the professor of modern history at Cambridge, has written several books on spying, including “Secret Service: The Making of the British Intelligence Community.”

He said there were “just too many” Soviet agents in Britain during the Cold War for MI5 to monitor effectively until 1971, when the U.K. expelled 105 suspected spies. After that, Britain became a “hard target,” with better capabilities of outmaneuvering the Soviets, he said.

MI5 was well-informed about Adolf Hitler’s intentions before World War II because of an agent in the German Embassy in London, according to the book. Agency officials, seeking to draw Prime Minister Neville Chamberlain’s attention to the threat, passed a memo to him saying that Hitler regularly disparaged Chamberlain.

The book describes the careful coaxing by the agency’s chief interrogator, William Skardon, of a confession from Klaus Fuchs, a German-born British physicist who worked at the Los Alamos, New Mexico, nuclear laboratory and passed atomic bomb secrets to the Soviets. Fuchs was convicted and jailed in 1950, in what was the “most important secret ever betrayed by a British citizen,” according to the book.

‘Glass Ceiling’

Andrew said that MI5 “smashed” the “glass ceiling” that slowed the ascent of women to top jobs well before private industry did. Several of its leading Soviet experts were female during the Cold War, as were two of its directors-general, Stella Rimington, who held the office from 1992 to 1996 and Eliza Manningham-Buller, who was in post from 2002 to 2007.

Lander, who was director from 1996 to 2002, said the book, which will be published in the U.S. next month, was “a cracking good read.”

Britain’s MI6 foreign intelligence agency has a similar project. It granted historian Keith Jeffery access to its most confidential papers, and his book covering the agency up to 1949 will be distributed next year by Bloomsbury Publishing Plc.

To contact the reporter on this story: Brian Lysaght in London at blysaght@bloomberg.net.

Last Updated: October 5, 2009 10:55 EDT