Death Watch Beetle aren't actually that rare in Britain. Not that common in modern houses, but in old buildings it's one of the things to worry about, especially for roof timbers, particularly oak. Normally the critters live in the wild, where they do a useful job in helping dispose of fallen trees and suchlike.

Most timber in modern houses isn't the type of wood they like, I gather - if it's not oak it doesn't suit their lifestyle or something.