The issue with morrisons veg oil is that Customs and Excise monitor sales of vegetable oil and if you don't contact them and pay duty on veg oil for use as motor fuel they come and molest you financially......
This blokes attitude was f**k em basically. I think if your subtle about these things and don't advertise you'll probably get away with it.
Or get a copper driving behind who notices the distinct smell of a chip shop !! lol