This section documents individuals prosecuted in Great Britain for espionage or assisting the enemy during the Second World War (1939–1945).
Most enemy agents captured in Britain were prosecuted under the Treachery Act 1940, emergency wartime legislation designed to simplify the prosecution of spies and saboteurs operating on British soil.
Treason and Allegiance
In certain circumstances individuals were instead prosecuted for High Treason under the ancient Treason Act of 1351.
Unlike the Treachery Act, a charge of treason required the prosecution to prove that the accused owed allegiance to the British Crown. This distinction meant that British subjects who aided Germany could be charged with treason, while foreign agents captured in Britain were usually prosecuted under the Treachery Act.
During the war four individuals were convicted of High Treason for assisting Germany:
- William Joyce
- John Amery
- Walter Purdy
- Thomas Cooper
Joyce and Amery were executed at Wandsworth Prison.
Purdy and Cooper had their sentences commuted.
The Treachery Act 1940
The Treachery Act 1940 was introduced during the invasion scare of 1940 to address the difficulties of prosecuting foreign spies under traditional treason law.
Under the ancient Treason Act of 1351, prosecutors were required to establish that the accused owed allegiance to the British Crown. This requirement complicated the prosecution of foreign agents operating in Britain.
The Treachery Act removed this obstacle. It made it a capital offence for **any person—regardless of nationality—**to assist the enemy in a manner likely to endanger British forces or military operations.
Conviction under the Act carried a mandatory death sentence, although in practice some sentences were later commuted or prosecutions altered when intelligence services judged a prisoner useful as a double agent, or when mitigating circumstances influenced the outcome.
Readers interested in the legal background of this legislation can consult my four-part article series on the Treachery Act.
Trials and Executions
Most espionage trials under the Treachery Act were held in camera due to national security concerns.
With two exceptions, defendants were tried before a judge and jury at the Central Criminal Court (Old Bailey).
Two agents — Josef Jakobs and Theodore Schurch — were tried by military court-martial at Duke of York’s Headquarters in Chelsea.
Almost all condemned spies were executed by hanging at Pentonville Prison or Wandsworth Prison.
The sole exception was Josef Jakobs, who was executed by firing squad at the Tower of London in August 1941.
Browse the Archive
The cases documented here fall broadly into three categories: agents who were executed following conviction, those who were turned and used in the Double-Cross system, and other espionage prosecutions from the period. A complete alphabetical index of all individuals is also available in the Master List of Spies.