"How does a festival organiser distinguish between the responsible owner and the irresponsible owner when they book and how do you answer the point that once the damage is done it is too late barring the irresponsible dog owner? "

Simple answer Dave - of course they can't. So yes, you are still allowing the risk of something bad happening.

In exactly the same way, when letting people drive their cars onto the site, festival organisers can't distinguish between the responsible driver and the irresponsible driver. So by allowing on all drivers they are allowing the risk of something bad happening.

The point I, and several others, have been trying to make, and which I haven't seen any reply from you on, is why the potential risk of a dog attack, however horrific, is somehow worse, or should be legislated for in a different way, than other risks? Is having your child attacked by a dog somehow worse than having your child run over?