I thought using cooking oil as an alternative to deisel was interesting enough to do some googling for:
There's quite a few sites dedicated to the subject such as:
http://www.greasel.com/General.htmlDon't go pouring veggie oil into your fuel tank without reading about it first.
Also, by law, any fuel you use to power your vehicle, you have to pay the fuel duty on. Even COOKING OIL if you use that to power your vehicle. Using it without paying tax, would be the same as using heating oil (which apparantly is the same as deisel, the only difference being it has a red dye added and is not subject to tax).
So cooking oil being a food is not taxed; until you put it into your vehicle; then it becomes liable for tax; in the UK.
I read somewhere that this was a bit like 'childrens clothing' which is also NOT taxable; purchased for use by a 'small adult', who then has to pay the tax on the clothing if he wears them!