How common is aggression in dogs in the UK?

Not a bad article.

This is the bit I found quite telling...

"The research also highlighted that although general characteristics, such as breed type, are significant risk factors across large populations they explain only a small amount of the overall difference between aggressive and non-aggressive dogs. This suggests that it is not appropriate to evaluate the risk of aggressive behavior in an individual dog using characteristics such as breed type."

Yes, I liked that part as well!