On 13 March 1961 at the Old Bailey Lonsdale was charged with spying, along with associates Harry Houghton, Ethel Gee and Morris and Lona Cohen (Peter and Helen Kroger). At the time of the trial British authorities were still unsure of his true identity. In March 1961, the defendants were found guilty, and Lonsdale received a 25-year sentence. He was to start his sentence at Winson Green Prison, Birmingham. From his single cell he fraternised with some of the Great Train Robbers. In due course, the British and American security services managed to establish his true identity as Russian citizen Konon Molody.