 By the end of the thirteenth century , several offences against either one 's lord , or one 's king , were treasonable . High treason , defined as <unk> against the sovereign , was first codified during King Edward III 's reign by the Treason Act 1351 . It clarified exactly what crimes constituted treason , following earlier , somewhat " over <unk> " interpretations of England 's legal codes . For instance , high treason could be committed by anyone found to be <unk> the king 's death or counterfeiting his coin . High treason remained distinct though , from what became known as petty treason : the killing of a lawful superior , such as a husband by his wife . Though twelfth century contemporary authors made few attempts to differentiate between high treason and petty treason , enhanced punishments may indicate that the latter was treated more seriously than an ordinary <unk> . 
