Glass's Information Services has found that although there has been some increase in demand for used LPG cars around London, there is no evidence of buyers paying a premium price.
Glass's forecast editor Jason King said: 'There may be some regionalisation of prices but, overall, residual values remain below those of petrol. Many potential buyers still have reservations about LPG, including safety and availability of supply. However, if other cities take up congestion charging, it might change the outlook for values.'
Martin Ward, national research manager at CAP, agreed: 'With LPG cars, even factory-fitted ones will be happy to get parity with non-LPG models. As for aftermarket conversions, nobody knows which are good and bad conversions, and dealers are being cautious.
'As for charging, there's no effect on prices because the average person in the street doesn't know what avoids the charge, even if the experts do.'
Malcolm Noyle, government and green fleet manager for Lloyds TSB autolease and head of the Clean Fleet Alliance, claimed a shift upwards in values has been taking place, particularly in London, although he agreed that more work had to be done on educating the public.
He said: 'In many areas, residual values for factory LPG cars are on a par or very close to petrol or diesel, and certainly are much closer than they were a few years ago. CAP has shifted its view and it has taken five years to realise there is almost parity between petrol and LPG. It will take perhaps another year before the retail public understands.'