Previously I’d noticed that at airports where agency staff operated the departure gates, they were much less likely to demand payment for passengers with wheelies in the Non Piority queue.

I'm currently at Luton airport (Swissport staff) - and they are going through the non priority queue and sending those with wheelys to make a payment !

they still don’t seem to worry too much about the size of non wheeled cabin bags - as long as passengers aren’t being completely crazy.