Slight drawbacks. Vegtable Oil when used in catering is food, in UK Zero VAT. As soon as you use it in a vehicle it is non food and subject to VAT at 17.5%. if caught exceeding the allowances by the Customs & Excise, bearing in mind they can test at random and can enter premises WITHOUT a warrant, deep do-do. Waste vegtable oil is classified by EEC as hazardous waste and requires a permit to dispose of it. Honestly you couldn't make it up. Sunflower oil is the best it is so volatile when hot that mills preparing it are classified an explosion risk. There is a large factory at Woolwich which prepares vegtable oils, great fun when 180 tons of the stuff decides to go bang. Though most diesels will run on SVO bear in mind the calorie count is much lower compared to Straight Diesel, and as far as I know only Bosch guarantee their injectors with bio diesel or SVO. I did it years ago on an old single cylinder dump truck, mixed the oil with paraffin. It does work but without a lot of grief it is really only an option on multi fuel engines. Straight diesels will probably need the injection timing doing.