It all depends on where the crew choose to base themselves. MAN base had a number of Northern Irish crew a few years ago, for instance. That base also has a number of Scottish and numerous ‘scouse’ (despite having a LPL base) crew and I guess all it takes is for the stars to align and you have a crew that you mistake for being based elsewhere.
Occasionally you will also get flights that, for whatever reason, are crewed by crew from two or more different bases.