What should I have done?

While driving home last night i happened to glance in to the carpark of a well trodden dog walk. To see to my horror a man beating a dog. I was traveling quite quickly on and a road that i couldnt stop without causing a rta. I turned round as soon as i could and drove back up. I swung into the car park and he was still there. He was a elderly bloke and a springer. The dog was sat next to car while the bloke changed his shoes the guy was using a crutch and seemed frail. I just sat there staring at him I had reacted on pure instincted and then really didnt know what to do. I watched him load the dog in the car and then i drove off. Today i feel bad what should or could i have done?

TBH there was nothing else you could do, by the time you got back he was no longer doing anything wrong. If you had gotten out and confronted him then chances are he would have lied and told you to mind your own bees wax.

First of all you need to be absolutely sure that the dog was in fact being beaten, for example could he have been drying the dog off, shaking out a coat etc?

Secondly if you got back into the car park, you could have taken a photo on your phone of him, the dog and the registration plate.

I would have to be very sure of what I witnessed before I reported anyone however.