Personally, I wouldnt give the RSPCA even a second of my time. Volunteered at a smaller horse rescue for 5 years though (would still be there if i had the time), thought the world of the RSPCA untill then, but realised just how useless they were once I started.
Ah, I wasn't thinking of doing it... just trying to trace a horse that went there. Long story but due to a message mix up I could have had him, didnt find out about him until it was too late and they'd taken him.