I'm glad that the UK has moved on from smacking and that it's illegal.
Little_Socrates makes a good point - it may be difficult to decide what is acceptable or unacceptable in every circumstance.
Suppose a child is about to run into the road. The parent grabs the child's arm, and yanks it back onto the pavement. If the child has bruises and a sore arm I could well imagine some pointless jobsworth bringing criminal charges against the parent. In Britain, authorities sometimes take almost perverse pleasure in punishing the innocent, while at the same time ignoring retarded aspects of BME cultures lest they be called 'racist'.