In August 2015, Christopher Andrew, professor of modern history at Cambridge and official historian of MI5 accessed documents released from the UK National Archive which confirmed that Belfrage worked for the Secret Intelligence Service (MI6) during the war and also spied for the Soviet Union [REF].
On 17 September 2015 a BBC Radio Four documentary "The Hollywood Spy"[REF] examined Christopher Andrew's allegations, but also put forward information by historian John Simkin that Belfrage was working for British Security Co-ordination as a double-agent, which would explain why he handed information to the Soviets [REF].