What about people who live in flats?
Personally, if someone was entering my house without consent in the middle of the night, I would have no problems smacking the crap out of them until they stopped moving. After all, I don't know if they might be carrying a knife and try to kill my girlfriend or - even worse - steal my TV.
The law is fairly lax on what "reasonable force" actually is. I reckon as long as they're alive then it's reasonable. They knew the risks when they broke in.
Here's a question - if you put a disclaimer on your house that says "if you break into this house you forfeit your right to prosecute if you are injured while on the property" would you be allowed to beat the living crap out of someone?
The idea came to me after that retarded case where a would-be thief sued the owners of the house he broke into for loss of earnings when they broke his arm or leg or whatever it was. A nice little legal plaque on the wall and you get free reign