Well those days are pretty much over now with the price of 100% pure veg oil now 98p per litre (up from 71p) - and - would you believe: Pura (until recently 56p a litre) is now £1.07 a litre.
Now, based upon an average mix of 50% that means that the potential saving has dropped from around £14.75 per tankful to £4.25.
Our smug smiles wiped from our faces then. I admit some use recycled oil, but I wouldn't. Soon the cost increases will filter down anyway.
The difference now means frankly I won't bother. The pump seals may welcome that decision...
So now with diesel so expensive, based on 6,000 miles per year, I will spend only £215 more in petrol for my BX or Fiat. Nothing like the margin before.