Recent revelations about secret mass surveillance programmes have raised fears about potential abuses of individual privacy in favour of national security.
With requests to intercept personal communications data on the rise, just who is collecting the information and for what purpose?
Even local authorities can now use surveillance powers to track employees and monitor the activities of residents.
So what rights do people have when they feel they have been unfairly targeted?
Jenny Chryss examines the role of the Investigatory Powers Tribunal - the little known body that considers complaints from those who've been under surveillance by the state.
Critics talk of an "Orwellian system" in which cases are shrouded in too much secrecy. The Tribunal usually sits in private, with claimants barred from hearing evidence and with little detailed explanation of its decisions.
So where should the balance lie between openness and effective oversight?

Producer: Gail Champion.