Not sure it is Bear, let me give you one example, a pub in london a few years ago was taken to court and ordered to admit an HIV positive customer. I recall the case in question. In any event it doesn'detract from the point I am making that venues asking for medical information is in itself not a breach of law, but the government cannot make it law in the UK. The same as, in the UK you do not have to tell a partner you are HIV positive but you do have to take precautions to keep you partner safe. If you do not disclose AND you do not use barrier protection you may be liable to prosecution. It, largley amounts to the same scenario, keeping prvate medical conditions that could potentially damage someone else.
I may not agree with the law in that example, but it is the law.