In reality the loss of red diesel will make very little difference on the rivers/canals as consumption is so low when compared to sea boats. Most river/canal folk would spend more money on beer whilst cruising than on diesel. A non issue.
In general the low tax anomaly is an indefensible argument with many folk struggling to pay £1.05/l to put in their cars to go to work. Blokes whizzing around in 30gall/hour £50k mobo who whinge about fuel price increases will be laughed out of court. RIP red diesel.
I'd best not start on the environmental aspects...................