Britain has been invaded as much if not more than any place worth living in on the face of the E, but the level of denial about that, usually referencing the natural alleged barrier of the surrounding seas, has been very great. The last successful invasion (not counting the Muzzie one, that hasn’t come to full fruit yet) was William and Mary’s “Glorious Revolution” which led to the overthrow of her brother James II, but the Irish “Book of Invasions” details various periods of recolonization after periods of wasteland, probably not entirely historical in character, and/or drawing on a prehistoric oral tradition dressed up with new names for the cast of characters and the groups to which they belonged.
Lots of people overlook that aspect of the Glorious Revolution. Sure, Parliament offered William the crown, but it was his Dutch army that secured it.
Oh, and then William went and invaded Ireland. :-))