Working my way through the internet as I do, I came across this bbc radio 4 program from April 4th 2010 called GCHQ: Cracking the code. As you probably know GCHQ is the UK's signals intelligence division so this is well worth a listen.

GCHQ: Cracking the code BBC Radio 4 2010-04-04 17:00 (UK listeners only I am afraid, but hey you know what a proxy is right?)

BBC summary:

"The BBC's Security Correspondent Gordon Corera gains unprecedented access to Britain's ultra secret listening station where super computers monitor the world's communications traffic and Britain's global eavesdropping and electronic surveillance operations are conducted."