I know there are some war period and history officianadoes hanging about here so if you don't know, the UK National Archives have made available a number of top secret documents from 1945 on line.
I haven't read these yet but there are supposedly the early details of the "Echelon" sigint agreement covering interception of calls.
http://www.nationalarchives.gov.uk/ukusa/ | Quote: |  | |
| The files contain details of the recently avowed UKUSA Agreement - the top secret, post-war arrangement for sharing intelligence between the United States and the UK. Signed by representatives of the London Signals Intelligence Board and its American counterpart in March 1946, the UKUSA Agreement is without parallel in the Western intelligence world and formed the basis for co-operation between the two countries throughout the Cold War. | |
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