Maybe the answer lies in enforcement. As this would cost money, franchise it out to wheel clampers. They have the skill set needed.
Unlicensed boats, over-stayers, and dumpers, could pay a fine, say £150 initially, and then if still non-compliant be towed to a location, away from anywhere convenient, padlocked and pay, say £500 to be released, and a storage charge of some £50 a day. With last resort, the option to gain possession, and sell the boat for non-payment. In addition, all unlicensed boats would need to pay all back fees, comply with the BSS and insurance, or be sold.
It would take a while for the message to sink in, but soon enough the problem would go away. CART, would refer all complaints back to the clampers. 🙂