It's common in the area. Went to a waterfall nearby, they also wanted twice the price, with a "half price for locals". Even after showing my ACR-I card that shows I'm a local resident, they refused. Not until I said I will remove their waterfall from the list of activities you can do while staying at Eden they let me in at the locals price.
Has nothing to do with money (think it was 100p/50p) but I hate the principle of dividing people based on ethnicity.