I think it’s just sheer bloody mindedness on their part Martyn. And I’ve only come across this at LHR. I once had to remove my shoes. Fair enough and through the scanner they went. I was without socks and the floor was cold. The shoes passed through and were put on the side. I politely asked if I could have them and was told in a sharp voice to wait my turn. There were a few people in front of me.
I asked again explaining I was barefoot and was told most aggressively “I told you to wait so you’ll do as I say”. I then took a photo of my feet and the floor and was asked what I was doing. I said it will make a nice story for the Mail. In a flash, with a smile and almost apologetically she gave me my shoes!
I could go on with other incidences that make no sense but I’ll leave it for another day.