Sair I make biodiesel....does'nt cost much and saves loads....
Old oil, heat up to around 50c, then add a mixture of methanol/caustic soda...mix for an hour....let it sit for about 12 hours, remove the glycerine(poss to make soap from this)....bubble wash numerous times...let it sit.....to remove excess water in the mix....
Put in car/van etc...money saved.
Thats about it....very easy proceedure....Sorry to sound slap-dash...but it is so simple....it is untrue....
The UK gov't will want about 27 pence per litre in tax....if you tell them

Dave.