A GM trial site in the region was found to have been contaminated with an unauthorised strain of oilseed rape.

The crop at Oakenshaw, near Crook, County Dur-ham, is among 12 sites in England to contain the unapproved rapeseed and will be harvested and destroyed.

The news comes as an investigation is under way after the same problem occurred in fields in Aberdeenshire, Scotland.

Aventis CropScience Limited, the firm which supplied the unauthorised strain, said the seed will not be used in future trials, though it believes it to be safe.

The batch has been traced back to a parent seed produced in Canada, though it has not yet been identified how it ended up in British trial sites. The Scottish Executive agreed that the rapeseed poses no threat to human health or the environment but said it was a "serious breach" of GM regulations.

The discovery has sparked fears over regulations of the GM crop trials, of which the autumn round is due to start on Monday.

A Scottish Executive spokesman said: "Aventis has been given very strong advice to make sure this doesn't happen again."

A spokesperson for Aventis said: "This is not a safety issue. However, we are taking this seriously and all crops will be harvested and destroyed, as with all trial batches."