was acting as a cover organisation for espionage activity were first aroused in 1925 when John Ottaway had tailed a suspect back to the Moorgate offices. The suspect Ottaway was following, Walter Dale, then went to the offices of the Federated Press, a Communist-controlled news agency for the American labour press which served as a journalistic cover for left-wing espionage in the UK. MI5 tapped the telephone lines of the FPA which revealed a raft of calls not only to Arcos but also suspected Soviet intelligence operatives, while interception of its post revealed copies of classified French dispatches. Arcos affair of 1927 On 31 March 1927, SIS (that is, MI6) passed evidence to MI5, courtesy of an informant inside Arcos, that Arcos had illegally procured and copied a classified Signals Training manual from the Aldershot military base. The British secret service also had testimony that the basement of 49 Moorgate contained photostat apparatus, for the purpose of photographing stolen secret documents. At 16:20 on 12 May 1927, a large force of uniformed and plain-clothes police officers entered the headquarters of Arcos and the Soviet Trade Delegation, located at 49 Moorgate in London known as the Russia House or Soviet House. The police took possession of the telephone exchange, detained all employees, and made a thorough search of documents on the premises. Drilling machinery was brought in to open locked rooms and strongboxes. They immediately proceeded to the basement they had been tipped off about, recovered numerous classified documents, found it to be rigged with numerous anti-intruder devices and notices forbidding entry, for which the employees had no satisfactory explanation. A secret cypher room was discovered, that had no door handle and could only be entered with a key, wherein workers were hurriedly engaged in burning papers. A struggle then ensued when police tried to wrest remaining papers from staff. The chief of this room then attempted to pocket a list, which on inspection detailed cover addresses used for secret communication with the communist parties of the North and South American, African and Australasian continents. A considerable number of documents were removed from the building in the course of the investigation. The raid and subsequent diplomatic incident subsequently became known as the Arcos affair. The next day, the Soviet Embassy handed in an official note of protest, stressing the illegality of the raid on Arcos headquarters. It was noted by the