The protections against any government department using surveillance unjustifiably are, in theory, considerable. Public authorities have to be "satisfied" that surveillance is "necessary and proportionate". Officials are meant to "consider the impact of these techniques on the privacy of those under investigation". Public authorities who use surveillance are "subject to independent inspection". The practice, however, has been very different. Officials frequently seem to think that they are justified in spying on private citizens if they suspect them of any violation, however apparently insignificant. That explains the hundreds of hours spent secretly observing whether people have been

recycling correctly, or have let their dogs foul the pavement.