That site Wikfgang linked to seemed to raise as many questions as it answered. One sentence seems to say one thing, the next seesm to say something else, the next something else again.

As Wolfgang says, travelling within the European Union passports tend to stay in your pocket. Even coming from England where technically you do need to have one. (That's, if you're white - getting back into England, if you're any other colour you'd better be prepared to show it.)