The full title of an article in 'The Register' is: How British spies really spy: Information that didn't come from Snowden:http://www.theregister.co.uk/2015/07...es_spy/?page=1

The author has assembled an open source jigsaw for this:
....the part-time Independent Reviewer of Terrorism Legislation, who in his day job is a high-flying human rights lawyer, also used his 373-page report to shed light on how spies use electronic surveillance, based on research that included a three-day visit to GCHQ in Cheltenham. This and other recently published documents provide new insights into how Britain’s electronic eavesdroppers work, and come from official sources rather than documents leaked by Edward Snowden.