please try to be at least a little curious about the due process surrounding how an elected Government decides when and where to execute people
The process was:
Troops in contact (Helmand?) = No, so no self-defence.
Hostile act? = don't know yet, intelligence-led.
Hostile intent? = You betcha!
Under certain cirumstances, proscribed enemy target sets can be engaged when not involved with any of the above, but it depends on the theatre-specific rules...