The SSPCA up here (local centre is in Drumoak, Aberdeenshire) are from my experience really pretty good.

Got our adorable wee cat from them, returned to full health, neutered, chipped and insured (for first month) for £50, (best fifty bucks we ever spent).
When he caught a sparrow, I rescued it and contacted SSPCA, they gave advice on what to do and phoned next day to see how it was (sad ending

).
There have been a few sad abandoned pet stories in the local press and it's usually SSPCA who come to the rescue.
Happy to support them and their good work.