There are wallabies on Lambay Island just north of Dublin, allegedly. Never seen them myself and was originally told about them by a drunken sailor, but have ha it confirmed by a more reliable source since :-)
Aren't there wallabies in the Chilterns? I was told they escaped from Whipsnade and have done quite well. Mind you, thinking about it, the source of this story was my Dad. He's full of tall stories about this sort of thing.