Genetically modified crops grown in the UK would have to be separated from non-GM fields by at least 35m (114ft), under proposals announced by ministers.
Every country in the EU is undergoing a consultation on GM
The measure is designed to minimise crop mixing should the European Union approve cultivation of GM crops.
Other proposals that appear in the UK government consultation paper include a public biotech crop register.
Pressure groups say the measures will not give consumers the choice of eating GM-free food.
Sue Mayer of Genewatch UK said the proposals were designed to limit "contamination" of non-GM crops to 0.9%.
European regulations mean that foods containing more than 0.9% of genetically modified ingredients have to be labelled as GM produce, even if farmers had set out to grow conventional varieties.
"Under the Department for Environment, Food and Rural Affairs (Defra) proposals, GM contamination of non-GM crops would be the norm, and a genuine GM-free choice won't be possible," said Dr Mayer.
"Another key question is the extent to which it is going to be possible to enforce and police any co-existence measures, particularly for crops such as oilseed rape which are grown on a large scale."
No commercial GM crops are currently grown in the UK.
The new proposals, launched by Defra on Thursday, seek to find ways to minimise unwanted mixing of GM and non-GM crops if and when the EU approves biotech varieties.
Other EU countries are going through similar consultations.
Defra's suggestions set minimum separation distances for any GM crops grown in England, ranging from 35m (114ft) for oilseed rape to 110m (361ft) for maize grown for human consumption.
They are designed to minimise unwanted mixing of varieties by cross-pollination or the dispersal of seed.
Defra is also seeking views on whether there should be a public crop register, and how to compensate non-GM farmers for any financial losses that might arise from the unwanted presence of GM material in their crops.
Launching the report, environment minister Ian Pearson said the government's top priority was to protect consumers and the environment.
"We have a strict EU regime in place which ensures only GM crops that are safe for human health and the environment could be grown in the UK," he said.
"No GMs suitable for UK conditions have met this requirement so far, and today's proposals are not a green light for GM crops."
But he said the government had a responsibility to be fully prepared if crops which met the safety criteria were developed and grown in the UK in future.
"That's why strict separation distances will be enforced so that organic and conventional farmers don't lose out financially and people can make a choice between GM and non-GM products," he added.
Some scientists are welcoming the consultation exercise.
Professor Philip Dale from the John Innes Centre in Norwich, UK, a leading plant research centre, said various groups had been debating the issue for five years or more, so the principles were well understood.
"Co-existence means exactly what it says; that different forms of agriculture will need to find ways of existing together," he said.
"This not only raises issues around food crops mixing with industrial GM crops but importantly also raises issues around high-value industrial GM crops being devalued by mixing with food crops."
Professor Guy Poppy of the University of Southampton said the consultation would allow the complexity of the situation to be considered.
"It is important that farmers have a choice of options available to them," he said.
"It is equally important that the public and other stakeholders can have their views heard and can choose how they want the land farmed."
Defra is seeking feedback on the proposals by 20 October this year. The consultation paper applies to England only; authorities in Wales, Scotland and Northern Ireland are responsible for developing their own policies.