Should the Government phase in the use of LPG as an alternative fuel?

LPG (Liquefied Petroleum Gas) is a clean and convenient source of energy in the UK that helps reduce emissions. Should the government make it compulsory for car manufacturers to only produce LPG run vehicles in the UK and phase out the supply of unleaded petrol and diesel over a period of say 3-5 years in much the same way they did with the old 4* Petrol.