Britain needs a radical rethink of its defences against emerging plant diseases brought in from abroad, such as the chalara fungus now threatening ash trees, the Environment Secretary, Owen Patterson, said.

Urgent measures need to be taken to prevent other infections being introduced, which might include setting up an international early warning system via British embassies, and stopping trees and plants being freely traded throughout the European Union, he said.

Announcing a series of interim measures to tackle the chalara problem, Mr Paterson said that in future, imported plant infections would have to be treated as seriously as imported animal diseases.