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 and this is managed differently by different endoscopy services, with some local policy requiring a medic being in the unit or in the hospital to allow a clinical endoscopist to work.