The crackdown reflects the police's belief that protests against road building and land clearance will continue to escalate. Deputy Assistant Commissioner John Howley, head of Scotland Yard's Special Branch, confirmed that this was a new police priority.
He said: "There are a lot of people concerned about the environment . . . We are primarily concerned about the extremists, those who for example put bombs under cars." He added that two recent examples of environmental activism were protests over the M11link road in east London and Twyford Down, in Hampshire.
The changing emphasis for the Special Branch, which is responsible for gathering intelligence about threats to national security, also reflects the end of IRA violence and the Cold War. They can now spend time on hitherto neglected areas.
Environmentalists argue that the vast majority of their actions are legal and peaceable and that the Branch is merely attempting to justify its existence.
Last month the publication of the Branch's new guidelines revealed that it was to spend more time monitoring public demonstrations and targeting animal rights activists.
The growing concern over "eco terrorists" follows the proliferation of environmental groups. There are now more than 140 local anti-roads groups.
Nationally organisations such as the Environmental Liberation Front and Green Anarchist have been credited with using booby traps to disrupt work at several motorway sites. The Freedom Network, a rainbow alliance of environmental groups, has helped uniteopposition against the Criminal Justice Bill.
Despite the IRA ceasefire, counter terrorism will remain the main focus of the Branch's work until peace is established.
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