Smacking may stop your child from doing something bad right now, but it won't teach him how to behave in the long run. Research suggests that children who are smacked are more likely to get depressed and have anger problems later on in life.
There have been calls for a complete ban on smacking in Britain. However, UK law does allow parents "reasonable chastisement" of a child, provided it doesn't leave a mark or bruise.
However, there are good alternatives when your child tests your limits. Try giving him a time-out, or temporarily take away a privilege or valued toy. For a toddler, clap loudly to get his attention. Then tell him off firmly saying, "No throw!" or, "No bite!"
Offer rewards when your child behaves well. Praise him, give him his favourite food for tea, or just give him a hug and some extra attention.