Following his release in 1953, Blake returned to Britain as a hero, landing at RAF Abingdon. In October 1954, he married MI6 secretary Gillian Allan in St Mark's Church (North Audley Street) in London. In 1955, he was sent by MI6 to work as a case officer in Berlin, where his task was to recruit Soviet officers as double agents. But he also informed his KGB contacts of the details of British and American operations, including Operation Gold, in which a tunnel into East Berlin was used to tap telephone lines used by the Soviet military. In order to protect Blake from exposure, the Soviet decided not to "discover" the tunnel until it had been in operation for nearly a year. According to the author of a 2019 book about the operation, the Soviets "valueBlake so much, they fear[ed his exposure more than they fear a breach of their secrets".