Fuel Bowsers
This is an extremely complex issue and very difficult to get a definitive answer. I recommend you book yourself onto a Dangerous Goods Driving Course - a company called Friendberry in West Country are v good but reasonable. Problem is the bowser has to comply with Aviation Law, Dangerous Goods Law (ADR), Environmental Law, Road Traffic Act and Trading Standards. Problem is very few people can advise on all these different requirements. For what its worth, this is what I found out - but don't take my word for it, check the facts yourself. Much depends on the size of bowser - If its capacity is 1000 litres or more, then you must be ADR qualified to drive it on the roads - it does not matter what quantity is actually carried. Exemptions under Limited Quantities do not apply. You must carry certain signs, equipment and your ADR licence and you will need information about the weight of your waggon train.
I took the point of view that we are actually carrying a lot of fairly nasty stuff so its wise to be conservative. If you have an accident whilst towing, YOU the driver will be the one prosecuted if you are not compliant.
Best people to talk to are VOSA in Swansea, talk to ADR section.
As regards bunding, few commercial tankers are bunded I believe, so I don't think its a requirement for the road, However it is a requirement under Environmental legislation that stationary bowsers inc those parked overnight should sit in a bund.
Hope this helps