Roger, Merve - LPG is a bi-product of oil production - it used to be burnt off as waste but now it is harnessed and used. Surely you can see that that is better than wasting a valuable resource.
As for it being as harmful as petrol or diesel - why then is it taxed at less than half of diesel and half of petrol because the DTI recognise that it is far greener than either.
Have a look at the DTI figs from their website:-
http://www.boostlpg.co.uk/driver_industry/why_LPG.htm
A short synopsis!
Environmental and social benefits
LPG is one of the cleanest vehicle fuels available, producing far less carbon dioxide than petrol and fewer particulates and nitrogen oxides than diesel. In environmental terms. Pan-European tests carried out on new vehicles in 2003 showed that for:
Global warming:
Use of LPG resulted in a 20%saving on CO2 over petrol and a 1.8% saving compared with diesel.
Air Quality:
On urban roads, on average, just one diesel vehicle emits the same fine particles as 120 LPG vehicles and the same NOX as 20 LPG vehicles.
LPG vehicles can help offset the considerable social costs of pollution damage to health and buildings.
You get a quieter ride with LPG; noise levels are 50% less than with diesel engines.
For more information, have a look at Environmental performance.
Economic benefits
You can save up to 40% off your fuel bill. Due to cuts in fuel duty, LPG retails for approximately half the price of petrol and diesel. LPG vehicles also qualify for cheaper road tax.
The Government supports LPG by reducing the level of fuel duty and by giving three years' advance notice in every Budget of any changes compared with petrol and diesel. This means that we know that the price at the pumps will continue at around half the price of petrol and diesel for at least this period.
LPG is better for your engine. Its simple chemical make-up means it's clean burning, and, as it is already in gaseous form when it enters the combustion cylinder, it burns more efficiently than petrol or diesel. Fewer deposits build up in your car engine, so it will run smoother and last longer.
Most cars having a petrol engine with spark ignition can be converted to LPG, but it is essential that you use a fully trained LPG specialist for the work. It costs around