For over half a century after the Bolshevik Revolution the term ‘subversion’, though commonly used around Whitehall, was never officially defined. Even the Security Service (MI5), though it had the lead role in counter-subversion for most of this period, was reluctant to attempt a definition. In 1971, the Director General (DG) of MI5, Sir Martin Furnival Jones, told the Conservative Home Secretary, Reginald Maudling, that he had ‘always refrained from trying to define subversion’. In the following year, however, the future DG, John Jones, then head of MI5 F Branch (counter-subversion), at last rose to the challenge, defining devised subversion as ‘activities threatening the safety or well-being of the State and intended to undermine or overthrow Parliamentary democracy by political, industrial or violent means’. This definition was officially, though inconspicuously, adopted by Harold Wilson’s Labour government in 1975, and reaffirmed by the Jim Callaghan government three years later.

Victor Madeira’s pioneering study of ‘Anglo-Russian Intelligence Wars’ during the twelve years after the Bolshevik Revolution provides a persuasive and vivid analysis of the period during which fears of Soviet-inspired subversion in Britain were at their peak. Even the usually non-alarmist British Prime Minister, David Lloyd George, declared in March 1919: ‘The whole of Europe is filled with the spirit of revolution.’ At various times subversion was believed to threaten to undermine the loyalty not merely of the British working class but also of the police, civil service and armed forces.

Dr Madeira is the first to integrate successfully the early history of British counter-subversion with the development of the British intelligence services which provided secret evidence of Soviet subversion. Some senior ministers were so alarmed by the intelligence they received that they were willing to compromise secret sources and methods in order to make it public. As Prime Minister during the Second World War, Winston Churchill attached enormous importance to protecting the Ultra secret – the success of British codebreakers in decrypting German communications – for fear that its revelation would do serious damage to the war effort. Twenty years earlier, however, he was willing to reveal what was then Britain’s most important intelligence source, the signals intelligence (SIGINT) derived from breaking Soviet ciphers.