There is no legal requirement for the physical presence of a medical endoscopist to be in unit for a clinical endoscopist to operate/scope.
Many units use nurse/clinical endoscopists to deliver weekend lists where there is no medic present or for community lists.
There is no specific JAG guidance on this. Different endoscopy services have different local policies, with some requiring a medical endoscopist to be present during a clinical endoscopist's procedures.