I used to have a very big VW camber, I ran it solely on chip oil, it stank like a chip shop outside and pinked a little but sooo cheap, I think I was paying 37p per litre, of course this was illegal, but... :-) you also had the option to buy the chip oil and pay the tax on it, so I would buy 5 gallons every now and then and just keep the receipt, it all came from the same pump, if I was stopped I would just show the receipt with tax paid. I would fill my camper up and I carried 5X 5litre Jerry cans that sat in a box mounted at the back. Cheap motoring :-)) this was bought at a special garage set up to sell this stuff, they processed it on the premises.