To mark the centenary of its foundation, the British Security Service, MI5, has opened its archives to an independent historian. This book reveals the precise role of the Service in twentieth-century British history, since its foundation by Captain Kell of the British Army in October 1909 to root out 'the spies of the Kaiser'.

'Sensationally good ... A riveting story, the real-life spooks and spies far more compelling than anything you will see on the screen ... history doesn't come more fascinating than this' Evening Standard

For over 100 years, the agents of MI5 have defended Britain against enemy subversion. Their work has remained shrouded in secrecy - until now.

This first-ever authorized account reveals the British Security Service as never before: its inner workings, its clandestine operations, its failures and its triumphs.

'Definitive and fascinating ... whether reporting on Hitler in the 1930s, the Double-Cross System of the second world war, Zionist terrorism, the atom spies, the Cambridge spies, the so-called Wilson plot or the 1988 shooting of the IRA bombers in Gibraltar, this book is essential reading' Alan Judd, Spectator

'The British Secret Service has opened its archives - and even 'insiders' may be in for a surprise ... magisterial ... extremely readable' Oleg Gordievsky, The Times

'Compelling ... a feast' Max Hastings, Sunday Times

'A superb account ... He has captured every important detail of the Service ... unlikely to be surpassed for another 100 years' Simon Heffer, Daily Telegraph