Re: do i need a passport to travel from the UK to barcelona??
We think N. Ireland is still part of the U.K. ?
Therefore , a passport should not be required for travel withing the same country , IMHO .
Albeit , Barcelona seems to still be in Catalunya , Spain , which also is a member of the Schengen agreement ( and U.K. is NOT ) ;
therefore : for Brits and other non-Schengen : valid passport = compulsory ;
whereas for the Schengen-group member states' citizens , a valid national ID card suffices .