Shame nobody has answered this one as I was going to ask a very similar question. I have been looking into the idea myself. One thing I have found out which is not a major problem, is that after 10 years you need to replace all of the gas fuel system parts. Other than that it looks pretty good, saves about 40% on fuel bills, there is a very slight drop in performance but the power delivery is better and its much better in terms of wear on the Engine. You can get a grant of �700 to put towards the cost of the conversion which costs between �1000 and �1500 for a standard car, if the car is less then 5 years old. Rather suprisingly its been around for some time, one place I was looking at did its first conversion in the 1950's. 70% of Japanese Cab's run on LPG so I think its pretty good. The one thing I would advise is check where your nearest LPG filling station is, you should be OK in big towns but where I live for example there isn't one for about 11 miles (of course a conversion will be dual fuel so you will still have your full tank of petrol to drive to your nearest station). They say the average driver will recoupe the cost of the conversion in about 2 years, if you do higher mileage, like me, of course it would be less time.