I am usually loath to enter into discussion upon the subject of gun control in the USA, but I am rather tiring of Americans misrepresenting the situation in the UK, for the purposes of justifying the preponderance of hand guns in their own society. As many people (both pro and con gun-control) have pointed out, direct comparisons between societies with considerably differing value systems are not always useful.
I fear the misconception articulated in your statement arises from a perhaps simplistic understanding of what constitutes self defence, and also what constitutes a life threatening situation.
Under Common Law a man is legally allowed self defence, and it is a patent nonsense to claim that in either in effect or in actuality, that constitutes a crime.
Self Defence: Legal Guidance: The Crown Prosecution ServiceThe basic principles of self-defence are set out in (Palmer v R,  AC 814); approved in R v McInnes, 55 Cr App R 551:
"It is both good law and good sense that a man who is attacked may defend himself. It is both good law and good sense that he may do, but only do, what is reasonably necessary."
The common law approach as expressed in Palmer v R is also relevant to the application of section 3 Criminal Law Act 1967:
"A person may use such force as is reasonable in the circumstances in the prevention of crime, or in effecting or assisting in the lawful arrest of offenders or suspected offenders or of persons unlawfully at large."
A person may use such force as is reasonable in the circumstances for the purposes of:
defence of another; or
defence of property; or
prevention of crime; or
In assessing the reasonableness of the force used, prosecutors should ask two questions:
1. was the use of force necessary in the circumstances, i.e. Was there a need for any force at all? and
2. was the force used reasonable in the circumstances?
Many other factors - to numerous to include here - are involved in the evaluation of self defence, but it is a very real section of British Common Law, and a tort upon which your own legal structures depend.
I am not about to instruct Americans about how they should conduct their society, but I would appreciate your not misrepresenting my own for your own political purposes. This has been done repeatedly in respect of both universal health care and gun control.