Dont agree with that one bit mate. And having a degree in forensic science i've done a little reading on the subject.
If someone comes into your house tonight and theoretically tried to stab you, are you going to block the blow with a shield made of "laws"?
In a perfect world your ideals would be just that but in the real world there are so many factors that could have influenced his decision to stab the intruders that its not even worth arguing whether it was warranted or not without knowing the relevant facts.
I am talking about the real world, the statistics are there for you to see. Go look at them, that's not student theory that's fact. This is murder, which means it has been looked over by forensics and all the other people who do the real jobs and determined not to be self defence. You studied it right, you know the difference between murder, manslaughter and self defence?
It is in uk law.
You missed out the part where I said in nearly any context. By law you are allowed to defend yourself with lethal force if you are being threatened with your life. This, however, is a murder case.