Fallow deer
There are six types of deer living wild in Great Britain: the Scottish red deer, roe deer, fallow deer, sika deer, Reeves's muntjac, and the Chinese water deer. Of those, Scottish red and roe deer are native and have lived in the isles throughout the Holocene. Fallow deer have been reintroduced twice, by the Romans and the Normans, after dying out in the last ice age. The other three are escaped or released alien species.