This is a very current issue in the UK. The current "coalition" government, which seems to be listing rightwards day by day, has proposed a loosening of the law covering what is a "reasonable" response to an intruder in one's home:
From the article:
"Can the intruder be chased if they run off?
"It all comes down to the fundamental question of what was proportionate in the moment and what the householder genuinely believed. If an intruder flees the scene, then at that moment they might not be presenting a threat to the householder any longer. This means that a householder who chases and attacks could no longer be considered to be acting in self-defence. Reasonable force can still be used to recover property or make a citizen's arrest.
"The Crown Prosecution Service (CPS) has suggested in the past that "a rugby tackle or a single blow would probably be reasonable" because these are designed to stop the criminal, rather than to inflict grievous harm."