Thanks Aviatrix for the update on the law.
I've been the subject of very offensive attitudes from staff at a large Newcastle hotel (beginning with C) when travelling on business with UK citizens, where I was treated like a potential terrorist when I declined to present a passport at checkin.
I am not required to have a passport to enter UK from Ireland and even if they had a doubt about me (I am over 60, female, lugging a laptop case and overnight case, so a really high risk profile ), I was clearly travelling with people they checked in with no questions.
Newcastle is no longer on my map, and somehow, I'm always busy when work in that area is offered.