My guess is too small as football shirts don't seem to compare with normal shop sizes. I would buy a large in shirts and T-Shirts but have to get an XXL in a football shirt. Not sure why that is, maybe due to modesty sizing these days.
That's my thinking. Trading Standards should advise more if you feel like getting in touch.
It's a different BHAFC in many ways from a few years ago and not all for the good.