Re: Telcos?
...GCHQ has a policy of not writing anything down if it can be avoided...
ALL the intelligence services have a policy of producing as little documentation as possible. This is because of their history - WW2 and then Cold War. During WW2, for instance, the SOE were famous for telling people as little as possible about what they were doing. And at that time there were very good reasons for limiting information distribution. Lots of people would get killed if the information got out, because you were in a total war....
This background and tradition is completely at odds with peacetime work - the rule of law, and the principles of justice which require examination of evidence in an open court. While the Police don't seem to be very good at this, they at least have the requirement for open evidence collection as a fundamental requirement for their work.
You might wonder why we still maintain an arm of the executive which operates secretly and ignores the law, given that we are no longer fighting a war for the continued existence of the country. You would be right to so wonder...