Not at the moment in England, Wales and Scotland, however given the direction of travel of environmental legislation it seems like only a matter of time before there will be. The UK government intended to ban red diesel for leisure boaters (red diesel is the name for the red dyed diesel which is sold at reduced tax rates) but reversed this decision for England, Wales and Scotland. One would expect that eventually this decision itself will be reversed to be consistant with the banning of new diesel cars in 2030 and the increasing number of low emission zones that are being established in british cities. Subsidised diesel already cannot be used by leisure boaters in the EU. Amsterdams' boats in its historic canals must go electric by 2025 and this transition is well underway.
So at the very least solar propulsion is definitely worthy of serious consideration if your diesel is coming up for replacement.