My twopennerth...
There are sections of the canal such as that I will transit today where 95% of the piled bank is either VM or lock landings, whereas the unpiled bank is, for the most part, unusable due to a combination of collapsed/shallow banks and vegetation.
The Shroppie shelf springs to mind too...
My fear is that this will roll out nationally on those sections where it is unworkable and bring a world of pain!
Also, I doubt that this scheme could operate within S17(3)(ii), the 5 mile stretch would need to be accepted as "other place the vessel can reasonably be kept" otherwise the Board risks constraining the distance over which one might navigate as I doubt in all faith that a fee could be seen to be influential in a decision as to whether a vessel might be navigating. Esp with Judge O'Malley's comments in mind.