However: No reason to be scared. We have that great, ingenious "List of invasive foreign species of European wide importance" (I hope the translation is roughly correct) that will solve all our problems...
(It will be interesting to see if Britains will follow that rule in future or if they will create own protecting regulations that are more efficient...)
@zoomaniac don't worry, they also include species not even kept in captivity and ones which naturally occur in small numbers in Europe to ensure that no introductions could possibly ever happen ever again!