Today's vandal will be tomorrow's hero

On Monday 30 Greenpeace volunteers chose to risk their liberty in an attempt to prevent the inevitable and irreversible pollution of our agriculture by genetically modified crops. A week earlier some 400 people did the same thing in a GM field in Oxfordshire, and on Wednesday a Genetix Snowball campaigner was sentenced for the same reason. Their decision to take this step is active citizenship of the kind Tony Blair should be promoting.

At Lyng in Norfolk, where the decontamination action took place, about 130 people crammed into the village hall three weeks ago, almost all of them to express their sometimes angry concern that a GM experiment could be carried out on their doorstep without their agreement - without even advance consultation. The farmer involved did not come to the meeting, did not hear those concerns and did not respond to them.

But standing up at a local meeting, in front of friends and neighbours, to criticise a powerful local figure like the local landowner takes a certain courage. A courage that deserves more attention from the media than that provoked by the temporary incarceration of one volunteer, lord or not. It is easy to satirise such protests as publicity-seeking; the harder question is why people have to go to such lengths to provoke so necessary a debate. Greenpeace has been flooded with calls of support from people thanking them for their actions.

The Government and the chemical industry, shaken, have predictably attempted to label us vandals. As the former roads minister Steven Norris once said: "Governments hate direct action, and that is why it is so effective". Governments hate non-violent direct action because it makes clear when a democracy is failing. Astonishingly, the peaceful removal of GM crops before they flower is practically the only democratic veto UK citizens currently have to prevent genetic pollution. At no point does the regulatory system for GM crops consult or seek public permission to proceed with these open-air experiments.

At no point have the people given their consent. Government has consistently ignored the overwhelming national mood against GM crops. The private interests of a small handful of chemical companies have been raised above the public's right to an uncontaminated environment and access to organic and non-GM food. Greenpeace has been campaigning for these trials to be stopped for 10 years - we know the dead-ends down every other avenue. So there was nothing reckless about Monday's action.

Throughout history, when the public has been ignored or disfranchised it has taken peaceful direct action, often of this interventionist kind, to change the rules. The examples are legion, and today's vandals often become posterity's heroes: from the Tolpuddle martyrs to Gandhi.

Greenpeace should know - we have acted to protect Antarctica from destruction and to prevent the North Sea from becoming a dumping ground for oil platforms, now officially banned in EU legislation. When government and industry have sanctioned the release of toxic waste into rivers, we have blocked pipes; when they have slaughtered whales in defiance of international legislation, we have disarmed their harpoons.

There is nothing new about these direct expressions of "people power": the American civil rights movement, the suffragettes around the world, the movement against the enclosure of common land, all found their legitimacy in the public acting together directly. More recently the movements to prevent road-building, the destruction of forests and the oppression of indigenous peoples have peacefully "trespassed", blockaded and intervened for the common good.

The non-violent direct action that Greenpeace engages in is not lawlessness - we act within strong moral boundaries. Our volunteers train in non- violence and do not react to violent situations such as being charged at with farm machinery. We accept responsibility for the consequences of our action, and have in the past had volunteers imprisoned for long stretches of time. In the case of Fernando Pereira, a Greenpeace photographer on board the Rainbow Warrior, who was murdered by the democratically elected French government, a life has been laid on the line in a peaceful protest against French nuclear testing.

With GM financiers entrenched deep within the corridors of power, only the actions of campaigners like Greenpeace offer the British people any hope that the public interest can be upheld. It may be that in a few years' time the UK public will be able to vote for a government committed to banning GM field trials, should that option be on the ballot slip. In the meantime, irreversible genetic pollution is seeping into our countryside and contaminating our food. Active citizenship keeps democracy healthy and responsive. Democratic governments should listen to it, not fear it.

The Government should also stop hiding behind the mask of science. There are many scientific arguments which show that unleashing unknown agents into the environment is risky. There was "no evidence" that pesticides, ozone-depleting chemicals, nuclear power, animal fodder and now GM crops caused problems - until it was too late.

Greenpeace is not, and never has been, against science. We have no objections to GM research, especially in the medical field, providing it is in the laboratory, in a contained environment. But large GM field experiments may cause irreversible genetic pollution, all for the sake of a product that is unwanted by consumers.

Agriculture is at a crossroads. We do not have the option of growing both organic and GM food. Planting fields with GM crops will contaminate wild plants and organic crops. The UK Agriculture minister has said that people have the absolute right to buy foods which are not contaminated by GM crops. Yet a recent report for the Ministry of Agriculture, Fisheries and Food by the John Innes Centre pointed out: "Once GM crops are released they, like all crops, cannot be completely contained." Farm-scale trials of GM crops deny people the choice of eating GM-free food, just as commercial plantings of GM crops would do.

Most people - MORI polls show about 80 per cent - do not want to eat GM food or have GM crop experiments conducted in their local environment. The market for GM crops and food in the UK is virtually non-existent and there is little prospect that it will change. By stark contrast, the demand for organic food is much higher than the supply: 80 per cent of organic fruit and vegetables eaten here are grown abroad. This makes no sense even as a business choice, let alone an environmental one.

The Government is spending pounds 3.3m of taxpayers' money on farm-scale GM trials. What we want to know - the reason we take peaceful actions that lead to imprisonment - is why?

Lord Melchett is executive director of Greenpeace UK.