To mark the centenary of its foundation the British Security Service MI5 has opened its archives to an independent historian. The Defence of the Realm" the book which results is an unprecedented publication. It reveals the precise role of the Service in twentieth-century British history from its foundation by Captain Kell of the British Army in October 1909 to root out the spies of the Kaiser up to its present role in countering Islamic terrorism. It describes the distinctive ethos of MI5 how the organization has been managed its relationship with the government where it has triumphed & where it has failed. In all of this no restriction has been placed on the judgements made by the author. The book also casts new light on many events & periods in British history showing for example that though well-placed sources MI5 was probably the pre-war department with the best understanding of Hitlers objectives & had a remarkable willingness to speak truth to power; how it was so astonishingly successful in turning German agents during the Second World War; & that it had much greater roles than has hitherto been realized during the end of the Empire & in responding to the recurrent fears of successive governments (both Conservative & Labour) & or Cold War Communist subversion. It has new information about the Profumo affair & its aftermath about the Magnificent Five & about a range of formerly unconfirmed Soviet contacts. It reveals that though MI5 had a file on Harold Wilson it did not plot against him & it describes what really happened during the failed IRA attack in Gibraltar in March 1988."