The collapse of the trial of the Ratcliffe coal protesters earlier this month has drawn new attention to police infiltration of protest movements. 

However, the controversy sparked by the exposure of undercover cop Mark Kennedy has been building for several years. While police have charged that environmental direct action represents a new and growing threat to public order, environmentalists have claimed the threat is being hyped to justify the growth of a labyrinthine and unaccountable intelligence structure under the control of the Association of Chief Police Officers (ACPO).

It is illuminating to re-examine the chronology of those debates in the light of what we now know about the activities of Kennedy and other police agents, thanks to a long running investigation by Guardian journalists such as Paul Lewis and Rob Evans.

ACPO created the National Public Order Intelligence Unit (NPIOU) in 1999, incorporating the pre-existing Animal Rights National Index. The move followed a report by Her Majesty's Inspectorate of Constabulary, which argued that some protest groups: "have adopted a strategic, long-term approach to their protests employing new and innovative tactics to frustrate authorities and achieve their objective. There is evidence that some elements operate in cell like structures in a quasi-terrorist mode to keep secret their movements and intentions." 

Mark Kennedy told the Mail on Sunday that he was recruited by the NPOIU in 2002.

A year later, according to the Guardian's account, he began infiltrating the environmental movement at the Earth First gathering on 12 August 2003. 

In 2004, the ACPO intelligence structure expanded with the creation of the National Extremism Tactical Coordination Unit, based in Huntingdon, Cambridgeshire, an area targeted by animal rights campaigners because of its research industry.

By 2006, the unit's head Superintendent Steve Pearl was claiming major success, suggesting that half of violent animal rights extremists were in jail and attacks had dramatically fallen off.

During this period, according to the Guardian, Kennedy was building up his position at successive Climate Camps, under the pseudonym Mark Stone:

But by Climate Camp 2008 – when activists gathered near Kingsnorth power station, in Kent – the undercover police officer's appetite for action was raising suspicions. Kennedy volunteered to be the driver in an action that saw 29 activists successfully hijack a train delivering 1,000 tonnes of coal to Drax. Behind his back, some protesters began calling him "Detective Stone".

Kennedy's actions are all the more significant in the light of his comment to the Mail on Sunday that "My superiors knew where I was at all times – my BlackBerry was fitted with a tracking device – and they sanctioned every move I made. I didn’t sneeze without them knowing about it."

Four months later, on 9 November 2008, the Observer warned of the growing threat from eco-terrorists:

The National Extremism Tactical Co-ordination Unit, which collates intelligence and advice to police forces, has revealed that eco-activists are researching a list of target companies which they believe are major polluters or are exacerbating the threat of climate change.

The unit is currently monitoring blogs and internet traffic connected to a network of UK climate camps and radical environmental movements under the umbrella of Earth First!, which has claimed responsibility for a series of criminal acts in recent months.

A senior source at the unit said it had growing evidence of a threat from eco-activists. 'We have found statements that four-fifths of the human population has to die for other species in the world to survive.

Two weeks later, the Observer's reader's editor announced the paper was withdrawing the story:

Environmentalist Keith Metcalf explained that Earth First! supported direct action against property, but not against people. He believed that the debate around sustainable population size had been twisted to imply that environmentalists wished to kill people.

He also repeated the belief of several others that Nectu was briefing in this manner in order to make prosecutions easier and to boost its funding, which is at risk owing to the decline in animal rights campaigns. I can't verify that or the fears about mass murder because, despite repeated requests, Nectu won't respond.

If the original article did not stand up, it did contain what George Monbiot called "a clue as to why the police might wish to spread such stories," for its authors had themselves stated:

The rise of eco-extremism coincides with the fall of the animal rights activist movement. Police said the animal rights movement was in 'disarray' and that its ringleaders had either been prosecuted or were awaiting prosecution, adding that its 'critical mass' of hardcore extremists was sufficiently depleted to have halted its effectiveness. Last Thursday a prominent animal rights activist accused of planting petrol bombs at Oxford University was cleared of possessing an explosive substance with intent.

The Guardian's investigative team put this suggestion to NETCU chief Steve Pearl:

Pearl denied the unit was engaged in mission creep but admitted that environmental protesters had now been brought "more on their radar" as they had been "shutting down airports, and shutting down coal-fired power stations, more recently stopping coal trains, hijacking coal trains and ships in the river Medway."

It now appears that one of the leading figures in stopping coal trains was Mark Kennedy of NETCU's sister unit, the NPOIU. 

Six months after Pearl's comments, police arrested 114 activists near Ratcliffe-On-Soar power station. The case against six of those activists collapsed earlier this month when Kennedy's role was revealed. The former agent has since claimed that he made tapes which proved the innocence of the defendants, but that these were withheld by police.

It is now surely hard to avoid the conclusion that many had already reached before the latest fiasco unfolded. Environmentalists have become the victims of out of control bureaucratic empire-builders, intent on carving out fiefdoms by criminalising legitimate protest.