Is self-defence an all-or-nothing defence??
Defendants do not need to wait to be attacked first; they can act preemptively.
However, those who use excessive force, even if some force was justified, cannot use this defence.
This can lead to convictions, with mandatory life sentences for murder, as seen in the case of R v Martin.
The Law Commission rejected adding excessive-force self-defence as a partial defence to murder, instead recommending an extension of provocation to cover such situations, now covered by the "loss of control" law.