AIR FILTER
LE
A mate of mine has a T Reg diesel car - he runs it on vegetable oil. He buys it in 5 litre tubs from Asda. It works out around 80p/Litre - even cheaper when there's an offer on.
On the negative side, anyone behind him will be permanently convinced there's a chippy nearby and will find their mouths filling with water without realising why...
Not to mention the authority's having a financial field day with him when he is caught , and then crushing his car for their own personal amusement!