This "bio-diesel" lark looks more and more interesting all the time: there is apparently a growing legal industry recycling waste fat into fuel, and one large supermarket chain is looking into the possibility of running its trucks off the stuff - that "chip shop on fire smell" could get more common.
It was somewhere down in Wales where the illegal diesel makers made the press, after the local Asda sold a year's worth of cooking oil in three months - they started rationing it to one litre per customer per day. There was a good Guardian article on the issue. But you might need an awful lorra lorra lard for aviation purposes...