MI5 was established (as the Secret Service Bureau) in 1909 in response to fears of German espionage. Over the next eighty years, MI5 identified numerous spies from Germany, the Soviet Union and other countries during the two World Wars and the Cold War. Foreign spies typically sought to obtain political and military intelligence, and during the wars some sought to carry out acts of sabotage.

Many of our files on these cases have been released to The National Archives, and three notable spy cases involving MI5 can be found below. These illustrate the differing motives and methods of spies, whether enemy agents or double agents run by MI5, and help to show the challenges that we have faced – and continue to face – in dealing with espionage.

• Carl Hans Lody was a German naval officer and spy in the First World War. He travelled to Scotland and Ireland to spy on the Royal Navy and British defences. However, he was caught two months after the war started. He was put on trial for "war treason", was convicted and sentenced to death. In November 1914, he became the first person in 150 years to be executed in the Tower of London.
• Eddie Chapman was a British career criminal who was captured by the Germans during the invasion of Jersey in 1940. He was trained as a spy by the Germans and was sent to Britain to sabotage vital aircraft factories. However, he switched sides and worked for MI5 as a double agent, deceiving the Germans with false information. He was so successful that Hitler awarded him the Iron Cross, Germany's highest honour.
• Klaus Fuchs was a German-born scientist who fled to Britain as a refugee from the Nazis. He worked on the Manhattan Project to build the first atomic bomb. He was also a communist and supporter of the Soviet Union and spied for the Soviets throughout the 1940s. His information helped the Soviets to build their own atomic bomb only four years after the Americans developed theirs. He was caught in 1950, convicted of espionage and sent to prison for 14 years.