The maize refused a licence by the Swiss government is currently being grown in the UK countryside in "farm scale trials" in Norfolk, Lincolnshire, Hertfordshire and near Reading.
Yesterday, environmental groups welcomed the Swiss decision and claimed it raised serious doubts about its cultivation in the UK.
"The Swiss seem to be taking the precautionary approach more seriously than us," said Dr Sue Mayer, director of GeneWatch, the genetic engineering watchdog. "If the Swiss have realised new concerns that have not been taken into account, then that throws the whole future of these trials here into question."
The Swiss ban follows a report by the country's Federal Bureau for the Environment, Forests and Landscape. The Bureau concluded that neighbouring farmers' fields could be contaminated by GM pollen.
The Bureau concluded: "The hybridisation of genetically modified inherited material must therefore be prevented. This could be greatly reduced by removing male blossoms from T25 maize prior to blooming. Even this process cannot guarantee that the pollen will not end up in a neighbouring maize field or be gathered by bees and emerge in honey."
It concluded that "harmlessness to humans and the environment has not been adequately proven and the risk cannot be sufficiently reduced by taking technical measures".
"This judgment shows the uncertainties and unknowns around genetic engineering," said Dr Doug Parr, campaign director of Greenpeace. "This new information raises serious questions about the approval of this crop. The field trials are unwanted. They should be stopped immediately."
The Government has licensed the growing of four fields of the T25 maize in Britain as part of a national testing system to assess its potential effects for the environment. The GM trials are being closely monitored by the Government prior to a decision whether to allow the commercial planting of GM crops in Britain.
Swiss concerns about the GM maize centred on its herbicide resistance and the fact that the GM plant contains parts of an antibiotic-resistance gene.
Scientists fear that the antibiotic-resistance marker genes could lead to resistance to several key penicillins used to combat fatal diseases such as meningitis.Reuse content