Im sure non British/Irish passengers on ferries would also need to produce a passport/id card...
No, you're the one clutching at straws. Anyone who has passed through immigration in Ireland knows that they tend to wave people through without much, if any of a check. So - our Polish friend has already managed to gain entry to the CTA without being known to the UK.
Then our Polish friend gets on a nice Bus Eireann waiting for him, headed to Belfast. The UK very, very rarely checks ID on the Irish frontier, so he's already in Belfast without any problems. Then.
Im sure non British/Irish passengers on ferries would also need to produce a passport/id card...
Why would they have to produce a passport/ID card when travelling inside the UK?
taken from stena line...
There is absolutely no obligation for them to carry any form of identity when sailing between Northern Ireland and Great Britain. Advised doesn't mean "required" - and a utility bill is hardly a form of identification. So - our friend has now entered Great Britain, all without a single check by the UK authorities.
I bet there's not alot of Poles working in Northern Ireland.
Erm...Belfast is full of them.
. So for a Pole to gain access to mainland Britain then they would be registered on the home office system. D.
Registered where, exactly? Given that there is no obligation to produce any identification when travelling on internal ferries, how could the Home Office know anything about our Polish friend?