Environment groups know they are being spied on and the arrest of 114 activists this week looks like more of the same

It was a beautiful, crisp, sunny morning in April 2005. At 6.30am the environmental group was just minutes away from its target – a Land Rover factory in the Midlands. The meticulously planned action involved people bursting through the perimeter gate, past drowsy guards and occupying the factory line. Little did they know that almost 50 policemen were already there, drinking cups of tea and waiting for them.

Fortunately for the activists, an advance guard spotted the helmets and the bus carrying the climate change protesters was turned round. It was obvious that someone had tipped off the police. There was simply no other explanation. The mole was identified and never allowed on another action.

This week it was almost certain that the 114 people arrested outside Nottingham were also shopped by an informer. Nearly a week before the action, police warned all power companies in the Midlands and the north that a major action against a coal-fired power station was likely and told them to increase security.

The police were also confident enough of their source to practically strip Nottingham of police and commit forward intelligence teams, get maps of the school and mobilise a helicopter. The operation involved some very senior officers. According to one person arrested, "this was not an ordinary police operation. We were set up. They knew where we were going and the resources used were immense."

Arresting officers openly said that they had known about the action for a week and that the operation was "intelligence-led". This could mean that the police relied on covert surveillance such as mobile-phone tapping, computer-hacking and vehicle tracking, but this is unlikely to have provided the authorities with reliable enough information. Much more likely, they used a traditional mole.

Environment groups know they are being effective when they are being spied on or infiltrated by the state or by corporations. Last year anti-aviation group Plane Stupid became aware that a man calling himself Ken Tobias was not a climate campaigner. He was set up, trapped and exposed as working for C2I security, possibly on behalf of the aviation industry.

Greenpeace UK has had a string of moles. Road protesters in the 1990s were spied on by a security firm employed by the government.

Last week EDF, the French nuclear company hoping to build several reactors in Britain, was charged with spying on Greenpeace in France. The McLibel 2 famously held one meeting where there were more moles working for McDonald's than there were activists.

But who tipped off the police about the Nottingham gathering? Precise information about the alleged action may only have been known by a few core people. It is just possible that they were infiltrated, but these people know each other well and have built the climate movement from nothing. Only a John le Carré mind could imagine such subterfuge.

Far more likely is that one of the 100 or more people "invited" to go to Nottingham was the mole. The climate movement welcomes new people and while seasoned campaigners went, for some volunteers it was their first action.

It was a dream for the police, corporates or anyone wanting to know what is going on. All a potential mole has to do is turn up to meetings, lie low for a year or so, fit in, show willing and gain trust and eventually someone will invite them on an action.

He or she probably had no idea which power station was actually being targeted, but all they had to do was nip out to the loo at a motorway service station and make a call or a text. By the time people had gathered at the school, the police would have known for certain which power station was the target. The clinching evidence of a low-level mole was that arrests were made not for "conspiracy to disrupt operations" at Ratcliffe-on-Soar power station (the alleged target of the action), but at an unnamed station.

Police surveillance of environmental activists has intensified since the demise of the animal rights movement and parallels the rise of climate change as an international issue with vast sums of money at stake. People going to public meetings are now liable to be photographed or stopped and searched.

Established groups such as Greenpeace and Plane Stupid have had their premises watched, and forward intelligence teams follow some people for months at a time. Many activist groups have complained that their websites have been sabotaged.

Rule 1 is to assume you are known. Rule 2 is not to communicate by email or phone.

Rule 3 is to beware moles.