GCHQ's intelligence successes rely upon staying ahead and maintaining an advantage over those that would damage UK interests. Therefore, it is most usually the case that GCHQ will not disclose information about their operations and methods. People sometimes think that we cannot be accountable but nothing could be further from the truth.
In fact, GCHQ is subject to very rigorous oversight both by Parliament and senior members of the Judiciary and works entirely within a legal framework that complies with the European Convention on Human Rights.
The Intelligence Services Act 1994 and the Regulation of Investigatory Powers Act 2000 underpin activities at GCHQ. The purposes for which interception may be permitted are set out explicitly in these Acts: national security, safeguarding our economic well being and the prevention and detection of serious crime.
Interception for other purposes is not lawful and we do not do it. The Acts also set out the procedures for Ministers to authorise interception; GCHQ follow these meticulously.