But the risk of it doing very much damage when it does spread far and wide need not be great.
Pollen is spread in one of two ways in a country like Britain - on the wind, or by insects.
How far it will travel by either method depends on what crop it comes from. Pollen from maize, the crop studied in the National Pollen Research Unit's work, is designed to be spread over a long distance by the wind. If you want to have no danger at all of pollination of other crops, then no barrier zone could prevent it. In theory, pollen can travel for hundreds of miles. At 200-m, it will not be very concentrated.