I have previously worked in a gateline role, and I find it better to take the "personal attack" out of interactions with people - they are usually just trying to get from A to B. Surely the selection process to the role, the training I get, and the pay I receive should insulate the public from my personal idiosyncrasies!
I try to remember people are human beings and sometimes that is more important than "rules"; in this scenario, I would have actively encouraged a mobility impaired person to come to the paid side of the gateline and into a seating area more suited to their needs away from the melee.
The OP has my sympathy, and hopefully gets a response from Chiltern that they are happy with.