103. 420?

Beginning with the capture of an agent named Owens, codenamed SNOW, MI5 began to offer enemy agents the chance to avoid prosecution (and thus the possibility of the death penalty) if they would work as British double-agents. Agents who agreed to this were supervised by MI5 in transmitting bogus "intelligence" back to the German secret service, the Abwehr. This necessitated a large-scale organizational effort, since the information had to appear valuable but in actual fact be misleading. A high-level committee, the Wireless Board, was formed to provide this information. The day-to-day operation was delegated to a subcommittee, the Twenty Committee. The name of this committee lead to a phrase regularly used in English vocabulary.

What is the phrase ?