The BBC's Robert Pigott: "The government says, companies are making significant concessions"

The ban will not be lifted until controversial farm-scale tests have been evaluated, said Environment Minister Michael Meacher.

But he admitted crops from the government trials could enter the human food chain before 2002, in products such as meat or milk, through animal fodder.

Mr Meacher insisted any such products would be properly labelled to make clear they came from animals fed on GM crops.

"We have a secure agreement with the industry that the produce will be identity-preserved throughout the chain," he said.

"So there is no question that we have other than a full public undertaking that there will be labelling for the consumer. No-one need eat any of this produce if they do not wish to."

Environment campaigners dismissed the assurances, but government officials said it was "highly unlikely" the crops would win the necessary European Union-level clearance to be used as fodder before 2002.

Protests

The ban, which had been anticipated, is being interpreted as a U-turn in government policy as a result of public protests against GM technology.

"This is a humiliating climbdown by the government and is obviously designed to distract attention from their disastrous handling of the beef crisis," said shadow agriculture minister Tim Yeo.

Liana Stupples, of Friends of the Earth, told BBC News Online that far from a U-turn, the move signified a continued commitment to GM crops.

"This announcement indicates that the government's foot is still firmly on the pedal, heading in the direction of the commercial growing of GM crops in the UK," she said.

GM test crops have been attacked by protesters

Patrick Holden of the Soil Association told BBC Radio 4: "The government's position seems to be that 'British biotech plc' needs to get a bite of this GM cherry as quickly as possible because their fear is that we will lose out on world markets."

But Mr Meacher said the government was neither for or against GM foods. He told the programme it was "perfectly possible" there would be no commercial growing of GM crops in Britain.

"There is no guarantee of commercialisation unless these results are wholly positive," he said.

The farm-scale tests are being carried out to assess the effect on the environment of GM crop cultivation.

Those opposed to GM crops fear pollen from the plants could spread from test sites and endanger naturally occurring plants.

Mr Meacher also announced that the voluntary agreement between the government and industry on the method of the farm-scale trials is to be renewed.

Plantings for the farm-scale trials are to be limited to 20-25 fields per crop per year. There is also a ban on the use of produce from GM crop trials for direct commercial benefit.

'Protecting health and environment'

Mr Meacher said: "The government has said all along that there will be no general cultivation of GM crops until we are satisfied there will be no unacceptable effects on the environment.

"This agreement is in line with our primary role which is to protect human health and the environment."

He said the agreement was not a ban or moratorium on GM crops as there were no legal, scientific or safety reasons for such action.

Up to now all the farm-scale trials have been in England, mainly Lincolnshire and Nottinghamshire. New sites are to be announced in February.