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.
The king has no power, that's why he's able to easily bend the national broadcaster and the police force to his will with ease ... that's why we have to get his consent to pass any laws ... that's why the armed services pledge allegiance to him (as monarch) and not to the UK ... that's why we pay him 100s of £millions from taxes ... that's why we organise a hugely costly parade for him in the middle of a cost-of-living crisis ... these are all signs he has no power /s