By Alex Kirby
BBC News Online environment correspondent
After five years of consultations and tests, UK ministers will today announce the fateful decision to allow GM crops to be grown commercially in Britain.
New dawn for GM crops?
They are expected to give agreement in principle to the commercial growing of one variety of GM maize in England.
The announcement will trigger vehement protest from anti-GM campaigners, and relief from the biotechnology industry.
But legal challenges and unanswered scientific questions mean crops are unlikely to be planted before 2005.
Agreement by all
The logical next step, assuming ministers give GM maize the green light on the basis of the recent farm-sized tests, is that the variety concerned, Chardon LL, will be placed on the UK Seed List (the national list of varieties).
Chardon LL is a type of fodder maize and it appeared to outperform conventional maize in the evaluations by allowing more wildlife to survive, although the result is contested.
But before any variety can be placed on the list, the devolved authorities in Scotland and Wales must agree with the UK government in Westminster that this should happen.
Neither is yet certain to give their agreement: the Welsh Assembly voted unanimously in 2000 to keep Wales GM-free.
The Soil Association, which has fought GM crops from the beginning, said it was fearful that if something went wrong, perhaps in 10 to 15 years, it would be "impossible to reverse".
Former environment minister Michael Meacher said the crops were "the wrong decision" because the science did not support it, the public was against it and it was driven by commercial interests rather than public interest for caution.
"There has been very little environmental testing, nothing about soil residue, nothing about gene flow from cross-pollination, nothing about the development of super weeds...and above all, there has been virtually no health testing of the impact of eating GM food on human beings," he told BBC Radio 4's Today programme.
Bob Fiddaman, spokesman for Scimac, a grouping of industry organisations that support GM crops, said the technology did not carry risk.
"Never has a form of technology been so tested and checked by scientists before it has been allowed to be fully developed," he told Today.
"There is nothing wrong per se with genetic technology because you're only moving genes within species."
As well as seeking agreement from Scotland and Wales, the government will also need to seek the approval of the Pesticides Safety Directorate for the chemical - glufosinate ammonium, marketed as Liberty - to be sprayed on the GM maize.
It may well say commercial crops must be grown in the same way as the trial GM maize used in the evaluations.
Two key contentious areas are co-existence (whether GM crops can be planted close to conventional or organic ones without contaminating them) and liability - who pays if something goes wrong.
Ministers want the industry to accept responsibility, but the biotechnology companies are strongly opposed to the idea.
The maize will face challenges
The probable result will be a government consultation stretching out over the spring and summer.
One possibility would see the announcement by the government of voluntary GM-free zones, though the technology's opponents say they would be unacceptable because they would be unenforceable.
If Scotland and Wales do agree to support a decision to let the maize be grown, that will not necessarily be the end of the government's problems.
It will have to advertise its intention to place Chardon LL on the seed list, and at this point it will be open to objectors to appeal against the decision. That could mean a hearing before a tribunal which could last for several months.
Pete Riley, of Friends of the Earth, told BBC News Online: "We would certainly appeal. This is a spring-sown crop, and the earliest possible date the maize could be planted is in early 2005."
None of this addresses the serious concerns many people feel about the farm-sized tests themselves.
Three days ago the House of Commons Environmental Audit Committee said approving GM commercialisation on the basis of the evaluations would be "irresponsible".
Images courtesy of Monsanto.