Comment by andrewla

UK common law as it pertains to "duty to retreat" and "self-defence", is largely a question for the jury. There is no fixed legal standard other than whether the actions were reasonable given the person's knowledge of the situation at the time.

The US tends to be a little more prescriptive, leaving a situation where different jurisdictions have more specific requirements for defining what constitutes self-defense.

Juries in the UK tend to have significantly more responsibility for making judgments like these, leading to a system where evolving views of what is right and wrong can result in standards naturally evolving over time, rather than being fixed by what people thought was okay thirty years ago.