Britain's Secret Intelligence Service grew out of the need to combat Imperial German and then Bolshevik Russian ambitions in the early part of the century. Its clandestine war continued against Nazi Germany. Under the leadership of Mansfield Cumming, it enjoyed spectacular successes like the breaking of the Enigma codes. However, this was offset by Cold War disasters such as its failure to identify Kim Philby as a double agent working within the MI6. Despite this, the MI6 has played a massive role in countering the Soviet threat during the Cold War years. Perhaps the last words should be left to General Yuri Kalugin, former head of the KGB: 'We had the impression that this was one of the strongest services in the world. Very sophisticated, very tricky, sly, scheming all the time and for that reason - dangerous.'