Just to clear up on the abused dog part...

At my shelter at least, the dogs are categorised in a traffic system; green, amber and red. The green ones are the gentlest and best suited to families, the reds need more experienced and patient owners, and the ambers are somewhere in between.

It won't be exactly the same system for all UK shelters, but I can guarantee that ALL rescue dogs' personalities and traits will be different. If you explain to the RSPCA workers that it will be your first dog and you are looking for a calm, gentle dog, then they will be more than happy to point you in the direction of one. Remember, the RSPCA is just as concerned about the dog's well-being as they are yours, if they think a dog isn't suitable for you, then they will advise you not to rehome it!

Good luck with your decision.