Ok I have a very small brain.
In a situation like this do we phone the police or the RSPCA first?
I think my first reaction would be to phone 999, we all hope that those three magic numbers will bring an immediate response.
Most of us carry a mobile phone around so maybe we should put the number in the phonebook.
I have to be honest, if I was alone I don't know if I would have the courage to confront the person in case there were drugs drink involved.
I would follow the person if I wasn't alone, if there were enough people around for it not to be obvious that I was following, or if I was in my car.

I'm sure you don't have a small brain at all!!! Good point to raise - I would definitely phone the police - they'll get there a lot quicker than the RSPCA (hopefully) The RSPCA have very little power in a situation like this - my understanding and experience of them is that they have to witness cruelty and neglect first hand in order to take action

I don't think I'd confront him first (unless I'd had a drink of course!!) because he might leg it and I'd want the s*d to be caught