MI5's understanding of Soviet espionage in Britain following the Bolshevik revolution in Russia was surprisingly limited and, according to MI5's own internal history, it had suspicions, but no proof, that between 1921 and 1929 there was a secret organisation in London headed by Jakob Kirchenstein,1 an American passport-holder of Lettish background who was a regular visitor at the offices of the Russian Trade Delegation. Surveillance on Kirchenstein had linked him to a pair of cipher clerks who worked in the building, and to various left-wing figures in the trade union movement. Certainly the Trade Delegation had been of interest to MI5 for years, and suspicions had been aroused at a very early stage when Nicolas Klishco had arrived as a senior official in 1920. Previously, he had landed in England as a Bolshevik refugee in 1907 and had been employed as a technical translator for Vickers, but he had been deported in 1918 as an undesirable. His brief reappearance in London, had made him a target for MI5 surveillance although no conclusive evidence was found to link him to espionage before he returned to Moscow in 1923, ostensibly to join the Foreign Trade Secretariat.