The Twenty Committee — the XX Committee, or Double Cross Committee — was the body responsible for coordinating British use of turned German agents. Under the chairmanship of J.C. Masterman, an Oxford don who documented the operation in his 1972 book The Double-Cross System, the committee oversaw a network of double agents who were feeding false information to German intelligence on a continuous basis.
By 1943, the British had effectively neutralized German intelligence operations in Britain. Every German agent who reached British soil had been captured or turned. This meant that German intelligence in Berlin was receiving, through its apparently functioning network of agents in Britain, a picture of British military dispositions and intentions that was substantially shaped by British intelligence officers.
The strategic value of this capability was enormous. It meant that the false information planted in the Mincemeat documents could be reinforced through other channels. Double agents could be used to confirm, in their reports to German handlers, that the information about Greece and Sardinia was accurate. If German intelligence received consistent signals from multiple apparently independent sources pointing to the same conclusion, the conclusion would be more credible.
Operation Barclay, the broader Allied deception plan for the Mediterranean theater, was designed to exploit exactly this capability. Barclay used multiple channels — double agents, diplomatic signals, simulated military preparations, false radio traffic suggesting unit concentrations, and planted documents — to create a picture of Allied intentions that was consistently false across all available sources of intelligence. Mincemeat was one component of Barclay, aimed specifically at the personal documents route through a neutral country’s intelligence chain.