I swear Ryanair introduced that knowing passports were not a legal requirement. So they over book seats knowing someone would have only brought a driving license with them.
"In fact, the flag of Northern Ireland makes up part of the Union Flag (Union Jack)." (Sorry can't remember how to do the italics thing ...)
No it doesn't as a matter of fact. The Irish bit of the Union flag is the cross of St Patrick.
As previously observed, some airlines make up their own rules about passports which in my view they have no business to. The fact remains you do not need a passport as a UK citizen to enter Ireland north or south.