Let's be kind and assume that the police officer caught trying to persuade an activist to spy on Cambridge University students who might be moved to protest, wasn't the sharpest tool in the box. For this is indeed the stuff of comedy. A officer sneakily trying to recruit a spy and not realising that all the while he was being spied upon himself. Once the embarrassment subsides, the officer may at least console himself with the knowledge that the young man he had singled out did indeed have the practical attributes for the job. Only the spirit was unwilling.

But this is also the stuff of nightmares. Put yourself in the place of that activist, cannily lured into entering the intimidating precincts of a police station – alien territory for him but the seat of power for the officer. Would you have the strength of will or presence of mind to resist that pressure, never mind the gumption to return wearing a camera? Citizens in a free society have a duty to act responsibly and to assist with the maintenance of law and order, but this police operation seems to be an outright abuse of power. One figure in a position of state-backed authority, surrounded by the trappings of that power. One figure drawn into a position of vulnerability.

The specifics of the Cambridge case will shock, but there is a now familiar narrative of how the secret snoopy state seeks to monitor the legitimate activity of those who might ask questions of it. This appears to be activity undertaken with little or no public consent or oversight. How much of this is going on? What are the guidelines? Are they adhered to by forces up and down the country? Is there central control? Who controls the information and how long is it kept? No doubt the Association of Chief Police Officers has rules but what do you know of the legislative framework? Who keeps the practice honest and ensures that the objective is the maintenance of law and order rather than the policing of irksome ideology? This week we learned of Green party London Assembly member Jenny Jones being monitored by Scotland Yard for attending legitimate left-leaning protest events. Are others so targeted? We don't know. We should.

But this is also another example of the attempt by those in power to enlist citizens as agents of the state. In universities up and down the country there has been a considerable effort to cultivate assets capable of monitoring young Muslim students considered at risk of radicalisation. The government's Prevent programme, and its deradicalisation arm Channel, has drawn on the university establishments themselves: lecturers and bureaucrats as surveillance assets. The result is predictable. Yesterday Ratna Lachman, director of the human rights group Just West Yorkshire, told a Society for Educational Studies seminar of fears that some universities have become "Islamophobic spaces" for those who now regard them as "extensions of the security arm of the state".

The government orders landlords to report illegal immigrants; property owners as surveillance assets. GPs to check the legal status of those they might treat; medical staff as surveillance assets. As the state shrinks in size, as the prime minister says it will, it needs an army of narks to engage in surveillance and policing in a different sphere. Maybe that's part of his big society.

Through the efforts of Edward Snowden, we now know the extent to which technology can be and is being used to monitor what we do. But while we grapple with the new, let's not neglect the scope and reach of traditional surveillance or forget that policing authorities – in noble cause – will often stray to the edge of the permissible. It starts with a man being groomed to spy on his mates at university, but where does it end?