I have never seen this in Ireland - ever. The only places I remember seeing something like this is in Australia, where there's a gorilla at the exit who makes you open your bag and looks inside (doesn't do anything besides look - never seems to touch). I usually try to wait till he's busy looking in someone elses bag and then go around the side.
Also in Chile and maybe Peru/Bolivia they had people trying to force you to leave your backpack either just at a desk, or in a locker. I usually pretended not to hear them and walk quickly past. If that didn't work and they followed me I would not understand spanish. If they tried to mime the action I would simply say 'No, Camera' and that would usually do the trick. I had $2000+ of camera equipment, not to mention priceless photos in that backpack, and I was NEVER letting it out of my sight. EVER!
I reckon that if I was told to leave my bag behind, I would say "No, but you are very welcome to walk beside me to make sure I don't steal anything", and see what response that gets. Or, tell them that it's actually just a disguise for a hideously deformed growth on your back, which if you take it off will make all the other shopers run outside puking their ring up.