If an angry man came into my house and I killed him with a hammer to the skull would I get done?

The legal test is always, was it reasonable force? What is reasonable? the law doesn't say but many years ago Lord Denning defined it as something the man on the Clapham omnibus would consider reasonable - in other words any disinterested third party. Yes it has to do with the nature of the attack upon the victim and its likely intent, the scale & ferocity of the attack, and what else you, the victim, might have done. If you were in genuine fear of your life the latitude you get is likely to be greater than if you simply killed an intruder. The law is unspecific, which is why the Daily Mail & others rail against house owners being prosecuted for killing burglars. Just because someone burgles your house doesn't give you the automatic right to kill them, only to restrain them - reasonably!