I do have personal knowledge of another area, where practice differs widely from one zoo to another.
Several years ago I sometimes visited zoos with my late brother who had Down's syndrome. As a disabled person he always paid a reduced entrance price, although the amount of the discount varied. As his carer, I sometimes got free admission, sometimes a discount, sometimes not. I didn't feel it was a big issue, but it might be important to some people. I note that Chester stopped giving free admission for carers several years ago, but Bristol and Edinburgh still do.
I have been checking a few websites and they do have information for disabled visitors on them. I would recommend checking the website before a visit and telephoning about anything that needs clarification.
Alan