The Government fears that existing security arrangements are not sufficient to protect a new phase of GM trials to be announced this week. It fears environmentalists could destroy the crops.
The move follows pleas for government help from biotechnology companies and farmers running the trials. They say they are unable to protect the crops from protesters' organised raids.
Local police forces have said they do not have the manpower or money to stop protesters attacking the crops.
The special GM forces will be trained in restraint techniques and in ways of protecting the fields from "eco-warriors". There will be patrols on each site and the Government has also considered installing CCTV cameras around the fields. The plans have been discussed in secret meetings in recent weeks.
Next year the Government plans to step up the tests with 75 trials of about 25 acres each, to assess the effects of the crops on wildlife and the environment. Ministers are understood to be furious about the direct- action campaign, which is jeopardising their assessment of whether to grow GM crops commercially in Britain.
Earlier this summer police arrested Lord Melchett, the Labour peer who heads Greenpeace in the UK, following a raid on a GM crop site. Among the protesters arrested with him was a former senior police officer who until recently was responsible for policing at the House of Commons.
At the same time police in London are planning a long-term war of attrition against environmental groups to weaken their power to mount direct-action campaigns.
Radical environmentalist groups such as Reclaim the Streets and Earth First! are the main targets, but, police sources suggest, well-established organisations such as Greenpeace could also be involved.
The offensive is signalled in a report by the Commissioner of the City of London Police, Perry Nove, into the Carnival Against Global Capitalism held in the Square Mile on 18 June. Parts of the demonstration degenerated into violence and 28 members of the public and 14 police were injured. More than 40 people were arrested.
The report, which accepts that some of the police's handling of the riot was "highly unsatisfactory", concludes that "the demonstration signals a new era of violent protest, which has implications for the whole country and for policing at a national level". It adds: "The aim is to achieve long-term attrition of the groups involved."
Reclaim the Streets was the "best known and largest group" in the demonstrations and Earth First! is also mentioned. A spokesman for the City of London Police said that the campaign aimed to "weaken groups involved in criminality", and that there was no intention of "disrupting or breaking up people engaged in lawful protest".
Tony Juniper, policy and campaigns director for Friends of the Earth, said: "It is pretty clear that the police are running a political agenda to disrupt groups that are running perfectly reasonable campaigns."
George Monbiot, founder of The Land is Ours, who has led non-violent protests and is a leading authority on genetically engineered crops, said: "I am staggered. I have come across many cases of surveillance and intrusive policing, but never such a bold statement that the police should take part in the political process. It is a very worrying development."
The Cabinet Office said that its security arrangements for the GM crops were confidential but ruled out bringing in the Army to protect the crops. "We do not discuss discussions we have held or security arrangements for the trial sites," a spokesman said.
Ministers have ruled out creating one giant isolated GM trial site for fear of attracting a permanent Greenham Common-style protest.