Without wishing to sound like a scratched record on this subject:
Report such sightings to the River Don Bailiffs
immediately That is what they are there for
If anyone has concerns about poaching of fishing illegally do something about when the event happens, not the next day on a forum
Whilst an answer may be forthcoming forum members can really only give a speculative answer, you may have witnessed such proceedings but we did not. Next time, if there is a next time, the bailiffs
are the people to go to
If you don't have their numbers send me a PM or email and I will quite happily forward their details to you
Your supposition that the person who let the fishing has an obligation to ensure people should use legal methods (as agreed by the Proprietors) is, in part, correct. If they had a printed ticket (which they
may or
may not have had) then the rules regarding the fishing should be on that ticket.
If not they can, legitimately if frustratingly, plead ignorance.
To an extent, therefore, the onus is on the person letting the fishing to make their ticket/permit holders aware of the rules and regualtions.
I hope that's helpful.