Firstly, You don't realize that by calling the RSPCA you would be sending those poor dogs to their next to certain deaths.
Secondly, have you tried contacting an animal shelter in your area?
Thirdly, Off the topic... I think that animals should never be called as possession and should always be referred to as companions... Also have you read through any laws for what you can do, because it may fall under making a citizens arrest. If it doesn't say that it acceptable then I think that we should be petitioning for this type of citizens arrest to be covered also, because many times animals continue to suffer because people have no proof to provide to animal protectionists so I believe that it should be legal to make I citizens arrest to stop it.
If I was you the next time I see this I would make a citizens arrest, and if I got arrested for doing so... Sure I'd go to jail, but there would be animal activists all over it petitioning for freedom and the right to conduct citizens arrest for if animals are being treated wrongly

so just a heads up if you do plan to do something crazy like this... Remember to tell people that you know to start petitions and contact all of us on this forum and any other animal rights activist organizations
[ADMIN Note: Name calling removed.]