The UK field trials of genetically modified (GM) crops are now in the last year of a three-year programme. The government has promised the crops will not be grown commercially until the trials are completed.

Even then, it will allow them only if it expects no unacceptable effects on the environment. But the level of opposition from protestors looks likely to grow further.

Several times trial fields have been taken over by protestors who have uprooted the experimental plants in order to prevent what they describe as contamination of other crops and wild species.

The government accepts that contamination ("cross-pollination") is happening, and that there should be bigger barrier zones round trial fields than at present.

But there is a wide gulf between ministers and campaigners on how wide the barriers should be.

Public consultation

At present the separation distance around GM fields is 57 yards (50 metres) for conventional crops and 219 yards (200 m) for organic or seed production.

The Environment Secretary, Margaret Beckett, said earlier this month: "There is a case for separation distances to be greater so as to ensure a maximum of, for example, 0.1% cross-pollination."

But Friends of the Earth (FoE) is among the critics saying this is nowhere near enough.

Adrian Bebb of FoE said: "The Government now admits that the separation distances around the GM crop trials are not large enough to protect neighbouring crops and honey from significant levels of GM contamination. The separation distance must be at least 3.1 miles (5 km)."

The government has asked the Agriculture and Environment Biotechnology Commission (AEBC), the independent UK advisory body on the issue, to organise a public debate on attitudes to genetic modification.

The Environment Minister, Michael Meacher, said the results would be taken seriously.

More warning

He told BBC Radio 4's Today programme: "Government needs to listen." He said public debate had always been "implicit" in ministers' thinking on GM crops, but added: "This isn't an easy issue."

But Pete Riley of FoE told BBC News Online: "I think there'll be more protests over this round of trials.

"The evidence on cross-pollination is stronger now than when the last round was announced.

"Last year the European Commission said a 5-km separation distance would be needed to ensure that oilseed rape production achieved a contamination threshold of 0.3%.

Wider appeal

"The government needs to be challenged to increase the distance with this round of trials: there's no indication that it intends to. I expect local communities will take whatever action they feel is appropriate.

"The government's giving us six weeks' warning before the first seeds are sown, and so people will be able to mount more effective campaigns."

Distrust of GM technology is widespread in much of Europe and north America, but appears not to be universally shared.

Last year, the global area of commercial GM crops reached 130 million acres (52.6 million hectares), 19% higher than in 2000.