Operating initially in Lisbon, he pretended to the Germans that he was in Britain. He fabricated reports about shipping movements, successfully convincing them. Eventually, he again made contact with British intelligence, and again offered his services. This time he was accepted.
Garbo reached Britain in the spring of 1942, and operated as a double agent under the aegis of the XX Committee. He purported to have recruited a large network of agents, including a number of influential people with 'inside' information. In order to foster this illusion, Garbo supplied the Germans with a certain amount of collateral information. The Germans then paid Garbo a large amount of money for this misinformation.
Garbo has the distinction of being one of the few people during World War II to receive decorations from both sides, gaining both an Iron Cross from the Germans and an MBE from the British.