As background info. The Sunday Times 08.05.11 has an in depth answer to a reader's question on converting a second hand car to LPG in their section of In Gear, Car Clinic, page 10. As other LOC members have pointed out the payback time seems to be too long if you convert a second hand car to LPG unless you do a high mileage [an example is given in The Sunday Times] A worry mentioned in the Times was 'When fuel duty rises again next January, it will go up by 1p a litre more for LPG than it will for petrol and diesel:according to HMRC , this is specifically "to reduce the differential with main road fuels". So LPG may not be so much cheaper for ever.'