In the late 18th century, Jeremy Bentham designed a building called the Panopticon. It was designed primarily for use as a prison. A single watchman stands in the middle of the building and can see every cell; however, the inmates cannot see the watchman. He is hidden behind a contrivance – some blinds, say. Although a cellmate is unlikely to be being watched at any given time, it is the possibility of being watched at the present moment that leads him to change his behaviour; he accordingly acts as though he is being watched all the time.
Many of the arguments against mass government surveillance – the kind that GCHQ carries out – are deeply ideological. Those on the left see their comrades fighting for something and join in. There are, however, very good arguments in favour of significantly reducing the powers of GCHQ which, as the Snowden files tell us, carries out espionage on a stunning scale.