With regards to diesel anyone noticed this bit of info.
From June 30th 2007 anyone using less than 2,500 litres of veg oil per year is no longer required to pay duty in the uk.
I'm currently using veg oil at 25% mix with diesel, no heater in my VW van, will be using at least 50% come summer. 20 litres works out too £14 and is supposedly cleaner.