Bill Oddie's Top 10 - Aliens

How much of our British wildlife is not actually British? Whether we realise it or not, a large proportion of our flora and fauna doesn't really belong here. These are Britain's aliens, introduced here from far away. Bill Oddie's mission is to count down what he considers to be the ten most welcome and the ten least welcome of these aliens. As ever, Bill's top ten results are likely to surprise or even shock.