The record on species introduced to the British Isles is rather mixed.

The European rabbit, introduced to Britain in the 12th century, eats and therefore damages a wide variety of crops and cost the UK £263 million.

Japanese knotweed, introduced as an ornamental garden plant in the late 19th century, the roots of which spread by underground rhizomes, can undermine and damage buildings, pavements and roads, cost £179 million.

The grey squirrel is a carrier of the squirrel pox virus which kills red squirrels but not grey squirrels.

The European crayfish is susceptible to crayfish plague which is spread by the introduced signal crayfish.

Of course it looks peaceful; dead squirrels tell no tales.