Jeez, those are some crappy figures guys, I'm getting minimum 14mpg average, and up to 19mpg on a run.
Assuming LPG is 20% less efficient as a fuel, and Unleaded is 83.9p, thats the equivalent of getting 22.9 to 31.0mpg on the same amount of Unleaded, which would never happen.
So, LPG means Diesel economy at Unleaded prices, a 3.9 V8, not a 2.5 in-line 4, and bags of power, torque, and a sweet sound.
Not to mention the reduction in CO2 emissions of 15%, and much cleaner in terms of environmental pollution.
If you want to run on Veggie Oil, do it properly, get an elsbett conversion to a diesel, then you're CO2 neutral and the engine will last. Plus your fuel will be something like 35p a litre from the cash n carry.
Obviously you'd inform Customs & Excise that you're using x amount of Veggie Oil as a road fuel per month, and pay the duty on it.
Upside is V8's are cheap second-hand, although an LPG conversion can be anything up to £2000 from a garage, and similarly a diesel may attract a higher price to buy, and properly converted to Dual Fuel Diesel/Veggie Oil could cost you £1000 for an elsbett conversion from a garage.
You pays your money and you makes your choice.
