Our van propelled itself all the way to Devon and some of the way back chomping on delicious biodiesel from a company in our neighbourhood called Uptown Oil. Uptown Oil delivers cooking oil to restaurants, then returns to pick the stuff up once it's served its purpose in sizzling up saveloys and the like. From an railway arch in SE1 the stuff is cleaned up for motor use. Uptown Oil is the only manufacturer of biodiesel in London, and their product is 10p cheaper per litre from what you'll get charged at BP and all its dirty brethren. What I like about all this is that it's an opportunity to use a resource for a second time, doubling its usefulness before it's deemed "waste". Recycling cooking oil in this way is much more efficient than raising crops specifically for use as biodiesel (a short-sighted tactic which means less food can be cultivated).
Drivers, start your engines.