Upvote:3
In The Jury and the English Law of Homicide, 1200-1600 T. A. Green outlines much of the history of modern British legal jurisprudence for murder. In summary:
Henry II's legal reforms eliminate the distinction between emendable and unemendable slayings, and the consequent concept of monetary compensation for the former. All felonious homicides became capital offenses punishable by hanging, with only a very weak, threshold, definition of malice necessary.
At no subsequent time was the employment of deadly force, other than in self-defence or certain judicial or quasi-judicial circumstance, legally acceptable behaviour.
So to address the specific question:
By the time of King Alfred it was already legally unacceptable in England to employ deadly force for the resolution of impromptu arguments. Punishment varied by era and circumstance, from hanging to monetary compensation, to forfeiture of property and chattels to the Crown as well as gaol time (in exchange for a Grace Pardon). One was, however, allowed to defend oneself from deadly attack, though at times only if physically constrained so as to make any thought of escape clearly impossible.
During the Plantagenet era there is overwhelming circumstantial evidence that, in general, juries crafted statements of facts found specifically to enable the finding of self defence for defendants regarded by the community as being of good character and substantial societal value. This practice disappeared after the Tudor legal reforms redefined trial juries, removing their evidence gathering power and beginning the modern practice of making them impartial arbiters of the facts.
Note also that for peers of the land, trial juries were composed exclusively of other peers of the land.