I fly to and from Britain about 10 times a year and I actually lived in Scotland for 5 years. I get stopped quite often by those guys, probably on the ground that I'm quite fair skinned but have a bushy black beard and hair and look quite intellectualish-nerdish. Then I hand over my Italian passport and they start asking if I've been to Syria, Lebanon or Palestine or the Middle East.
I answer with my best possible Glasgwegian accent that no, i've never been there and that I'm a software developer living on the continent catching up with my dearest mates and girlfriend back in Maryhill and that mainland europe is terrible and i'm moving back the soonest, honest.
Then they laugh and let me go.
On the other side, when I go through border control wearing a palestinian kefiah they never stop me.
They're a leftover of the civil war in Ulster, apparently trained in remembering all the mugshots of IRA-affiliated people. Now they're a bit useless I guess.