Fruits for labour

Alan Johnson's plan to give pregnant women cash to buy fruit and vegetables makes sense from a nutritional point of view. And I can see why it is right not to load it down with bureaucracy by creating, for example, more tax credits. But couldn't they provide £100 worth of fruit and veg vouchers - or a debit card - that would be accepted at any supermarket or fruit and veg store instead? And couldn't it then be rather better targeted?