I was under the impression you don't need a passport to travel now that we are all part of the EU... but... you do have to have some ID that is recognised in the coutry you are travelling, e.g. a passport... more recently, if you have an EU style driving license, this will be OK but thats about it as far as 'shared ID' goes. Now in the UK, its not law to carry some sort of ID, so its probably ok for europeans to travel here without any ID at all...