Uninvited guest will be asked to leave, if this request is ignored, reasonable force will be used ie i'll break your F*****g neck.
In answer to your question, you can use reasonable force, this is open to interpretation tho, it depends on the threat that is being posed, for example, if someone came at me with a knife, i would'nt hesitate in using a baseball bat on them, now thats reasonable to me
Reasonable force generally means the use of force required to defend yourself or possibly detain.
So for example hitting an intruder with a handy blunt object would be OK, continuing to batter him while he lays bleeding and helpless on the ground is not.
Similarly shooting an intruder in the back as he tries to escape (like a certain famous farmer did) is not OK especially if it's with a banned firearm.
It's also not OK to lay traps inside your house, so for example laying gin traps just inside windows in out.
Best defense is a good set of locks and an alarm. Burlars are notoriously lazy and can spot a hard target a mile off .
You'd need a very good solicitor. I don't think you would get away with using an actual weapon (gun, knife etc.), nor going too far and actually killing the intruder. You'd have to argue that you used whatever weapon came to hand, and that you only intended to immobilise them - if you just happened to kill them altogether then you'd need to argue that you didn't intend to.