I don’t know how it evaded my attention at the time, but somehow it did. Back in June, Her Majesty’s Revenue and Customs simplified rules for producers and users of biodiesel such that if you produce (or use) less than 2500 litres per year you are exempt from fuel duty, and from the requirement to fill out monthly returns.
This translates to a potential tax saving of £708.75 (28.35p duty per litre x 2500), and makes using vegetable oil as a diesel substitute a whole lot more attractive.
My friend Jake is currently trying out a blend of 20% vegetable oil, 80% diesel in his unmodified VW Polo and has so far driven 600 miles with no side effects!
Since Vegetable oil is about £0.55 per litre (compared to over £1 a litre for diesel), even this 1:4 mix is saving him around £4 per tank.