In UK the king has absolute power, its just that they don't exercise it because in a civilised country they would need to be guillotined afterwards.
Of course we do, the order would be ignored. (To whom would he even give the order?) English history is written in constitutional crises.
Well, the death penalty was abolished in the U.K. in the 1990s, so there's that. More significant: habeus corpus, which goes back to somewhere between the Magna Carta and Interregnum.
Even at its height, the Crown's power to unilaterally command executions was intentionally curtailed for centuries.