When you hear the term "domestic extremist", whom do you picture? How about someone like Dr Peter Harbour? A retired physicist and university lecturer, he worked on the nuclear fusion reactor run by European governments at Culham in Oxfordshire; he's 70 next year, and has never been tried or convicted of an offence, except the odd speeding ticket; and he has never failed a security check. Not the sort of person you had in mind? Then you don't work for the police.

Dr Harbour was one of the people who campaigned to save a local beauty spot - Thrupp Lake - between the Oxfordshire villages of Radley and Abingdon. They used to walk and swim and picnic there, and watch otters and kingfishers. However, RWE npower, which owns the nearby power station at Didcot, wants to empty the lake and fill it with pulverised fly ash.

The villagers have marched, demonstrated, and sent in letters and petitions. Some people tried to stop the company from cutting down trees by standing in the way. Their campaign was entirely peaceful. But the power company discovered that it was legally empowered to shut the protests down.

Using the Protection from Harassment Act 1997, it obtained an injunction against the villagers and anyone else who might protest. This forbids them from "coming to, remaining on, trespassing or conducting any demonstrations, or protesting or other activities" on land near the lake. If anyone breaks this injunction they could spend five years in prison.

The act, parliament was told, was meant to protect women from stalkers. But as soon as it came on to the statute books, it was used to stop peaceful protest. To obtain an injunction, a company needs to show only that someone feels "alarmed or distressed" by the protesters, a requirement so vague that it can mean almost anything. Was this an accident of sloppy drafting? No. Timothy Lawson-Cruttenden, the solicitor who specialises in using this law against protesters, boasts that his company "assisted in the drafting of the ... Protection from Harassment Act 1997". In 2005 parliament was duped again, when a new clause, undebated in either chamber, was slipped into the Serious Organised Crime and Police Act. It peps up the 1997 act, which can now be used to ban protest of any kind.

Mr Lawson-Cruttenden, who represented RWE npower, brags that the purpose of obtaining injunctions under the act is "the criminalisation of civil disobedience". One advantage of this approach is that very low standards of proof are required: "hearsay evidence ... is admissable in civil courts". The injunctions he obtains criminalise all further activity, even though, as he admits, "any allegations made remain untested and unproven".

Last week, stung by bad publicity, npower backed down. The villagers had just started to celebrate when they made a shocking discovery: they now feature on an official list of domestic extremists.

The National Extremism Tactical Co-ordination Unit (Netcu) is the police team directing the fight against extremists. To illustrate the threats it confronts, the Netcu site carries images of people marching with banners, of peace campaigners standing outside a military base, and of the Rebel Clown Army (whose members dress up as clowns to show that they have peaceful intentions). It publishes press releases about Greenpeace and the climate camp at Kingsnorth, in Kent. All this, the site suggests, is domestic extremism.

Netcu publishes a manual for policing protests. To help identify dangerous elements, it directs officers to a list of "high court injunctions that relate to domestic extremism campaigns", published on Netcu's website. On the first page is the injunction obtained by npower against the Radley villagers, which names Peter Harbour and others. Dr Harbour wrote to the head of Netcu, Steve Pearl, to ask for his name to be removed from the site. Mr Pearl refused. So Dr Harbour remains a domestic extremist.

It was this Paranoia Squad that briefed the Observer last month about "eco-terrorists". The article maintained that "a lone maverick eco-extremist may attempt a terrorist attack aimed at killing large numbers of Britons". The only evidence it put forward was that someone in Earth First! had stated that the world was overpopulated. This, it claimed, meant that the movement might attempt a campaign of annihilation. The same could be said about the UN, the Optimum Population Trust, and anyone else who has expressed concern about population levels.

The Observer withdrew the article after Netcu failed to provide any justification for its claims. Netcu now tells me that the report "wasn't an accurate reflection of our views". But the article contained a clue as to why the police might wish to spread such stories: "The rise of eco-extremism coincides with the fall of the animal rights activist movement. Police said the animal rights movement was in disarray ... its critical mass of hardcore extremists was sufficiently depleted to have halted its effectiveness." If, as the police maintain, animal rights extremism is no longer dangerous, it is hard for Netcu to justify its own existence - unless it can demonstrate that domestic extremism exists elsewhere. A better headline for the article might have been: "Keep funding us, say police, or civilisation collapses".

Netcu claims that domestic extremism "is most often associated with single-issue protests, such as animal rights, anti-war, anti-globalisation and anti-GM crops". With the exception of animal rights protests, these campaigns in the UK have been overwhelmingly peaceful. As the writer and activist Merrick Godhaven points out, the groups whose tactics come closest to those of violent animal rights activists are anti-abortion campaigns. The UK Life League, for example, has published the names and addresses of people involved in abortion and family planning. Two of its members have been convicted of sending pictures of mutilated foetuses to doctors and pharmacies. Anti-abortionists in the US have murdered doctors, nurses and receptionists. Yet there is no mention of the UK Life League or anti-abortion campaigning on the Netcu site. This looks to me like partisan policing.

Just as the misleading claims of the security services were used to launch an illegal and unnecessary war against Iraq, Netcu's exaggerations will be used to justify the heavy-handed treatment of peaceful protesters. In both cases police and spies are distracted from dealing with genuine threats of terrorism and violence.

For how much longer will the government permit the police forces to drum up business like this? And at what point do we decide that this country is beginning to look like a police state?

monbiot.com