What is now often referred to as “lawful interception” has been a feature of British life for centuries. As early as 1324, Edward II issued a writ demanding that couriers entering the kingdom carrying letters be imprisoned and their letters forwarded to the King.
Queen Elizabeth’s Secretary, Sir Francis Walsingham employed a cryptanalyst, Thomas Phellipes, who was responsible for decrypting intercepted messages. It was his decryption of messages sent by Mary, Queen of Scots, which led to her execution.
Cromwell established the first effective postal monopoly in the UK, and after the Restoration a further Act of Parliament confirmed the monopoly and authorised the opening of selected items of mail under warrant "to discover and prevent many dangerous and wicked Designs . . . the Intelligence whereof cannot well be Communicated but by Letter”.
This practice continued until 1844, when a scandal over the forwarding to the Austrian Ambassador of the contents of the intercepted letters of an Italian exile in London caused the existing “Secret Offices” to be closed down. As Britain's unchallenged naval superiority and its growing material prosperity grew, Victorian statesmen became able to dispense with the need for intercepted information for intelligence purposes, though the military, both in the UK and in India, began to glimpse the possibilities offered by interception and decryption from the time of the Boer War onwards.