I am often asked if I get into a confrontantion and I have to defend myself, or loved ones, when do I stop, and where do I stand under UK law. The following was included in one of our newsletters some time back but I feel it's still just as relavant.
ONCE YOUR ATTACKER STOPS SO MUST YOU
Remember, the law will not be on your side if you use excessive or unnecessary force. That is, more than is necessary to stop or ward off an attack. Just how much force needed is impossible to state, as circumstances and attacks vary. At the end of the day only you can decide how much force is necessary. Always err on the side of safety.
The law clearly states that you are entitled to preserve life but you are only entitled to use reasonable force. Keep in mind what is reasonable for one person might be unreasonable for another. However, if it can be proved that you are the innocent party you therefore have the right to use as much force as is necessary to halt your attacker. Once he has been deterred or subdued, you must not do him any more harm. Move away and sound the alarm.
It doesn’t matter how much pain you inflict on your attacker so long as you use no more force than is necessary to stop him attacking you. If you continue after he has stopped the law is on his side. At the end of the day you are responsible for your own actions and you will be the one to pay the consequences for any action you take. If you injure him severely you will have to justify your actions and prove that it was necessary. At the time of conflict only you can decide when to stop.
However, bear in mind "It's better to be judged by twelve, than carried by six!".