Just saying you thought you saw a weapon and if you only hit him once (or a couple times if he is getting back up, ie dont keep beating him on the ground out cold). The reason the cases where people were deemed to have overstepped "reasonable force" happened is usually because the robber is trying to run, they are beaten to death after being KOed or similar scenarios where the other guy is clearly not fighting back. One single blow to the back of the head is no more suspicious than the side or front, if anything it proves you are more scared of confrontation. A well worded excuse like "i heard a noise, went to investigate taking the bat just in case i needed to scare someone off, then i saw the burglar and i (thought i) saw him holding a weapon (hammer is prob a good one) so i hit him once and he fell to the ground and i called 999" would make it extremely difficult for them to even take the case to trial let alone convict in front of a jury. Also of course never speak to police without a solicitor there. Im not justifying killing the burglar as i believe in self defence and not vigilanteism, but you can be as safe as you need to be as reasonable force is open to such a wide interpretation and if you feel youre life is in danger then it is in danger. Now if the guy was just a teenage kid who was unarmed you wouldnt crack him in the back of the head, either warn him off or wing him taking out his knee and call the cops, whatever is reasonable at the time, but the point is the law is designed to allow you to protect yourself as much as possible, you just cannot carry offensive weapons in public which is an entirely separate collection of laws. As the saying goes, with the support of the Mail less time you will spend in jail. They got Tony Martin out on a much reduced sentence and he did himself no favours using an illegal shotgun to shoot someone in the back outside of his house as they ran away from him. This is the most recent debate worthy case on the topic: http://www.guardian.co.uk/uk/2009/dec/14/jail-brothers-burglar-cricket-bat Pesonally i think the sentences were spot on and they clearly overstepped from self defence to revenge but even that case got public outcry for them to be found innocent (due to the attack on the family which was horrific i do not deny).