fat oil / red fuel use increase a cert
Another issue is that chip oil is mostly veg oil which is also spiralling in price. The "bio"fuel makers are only just staying behind the price of regular fuel.
We have a biofuel company in one of our buildings and they have halted production for the time being, they can produce it for around 95p/litre atm (inc road duty) - most people cant be arsed for that kind of saving.