not entirely true
as the gentleman is a UK citizen he will not have a national identity card
As I said - "either a passport or a national identity card". Some may have both - I know someone who has a Dutch ID card and British passport, for reasons best known to herself.
I suggest ignoring internet know it alls who dont even register and are pretty obviously not UK residents as we all know you cant get out the friggin country without a passport......Oh, and that there is no such thing as a national identity card in the UK,as for the Polish end of things,pass.
Some countries do give you an extra once over if you are on a short passport but I doubt one EU country would bother for another EU country.
I said "either" :P
(you actually could leave on a UK ID card - they were produced and issued to a small amount of people, but I think they've now been annulled).
It certainly used to be the case, and the police can ask for ID at any time, but nobody is ever prosecuted for not carrying one.
Actually - I know someone who got a 50PLN fine for not having it. But that was after getting stopped for crossing on a red light - so he ended up with 2 50zl fines :)
As far as I understand it, the general idea in Poland is that you must carry *something* - be it a scan of a passport, a driving licence, etc.