DUAL-fuel vehicles will be obsolete within five years because they will not keep pace with the environmental improvements offered by traditional petrol and diesel engines, according to shock predictions from leading industry figures. The controversial forecast made at an international forum on alternative fuels will send shockwaves through fleets and manufacturers which have invested millions in 'green' vehicles.

It also questions the Government's investment in grants and tax incentives for clean-fuelled fleets. The predictions, from David Lang, chief engineer of the Automobile Association, and Andrew Eastlake, manager of powertrain engineering at Millbrook Proving Ground, have been rebuffed by manufacturers and fuel providers. Suppliers have invested heavily in creating a market for clean fuel vehicles and still predict that clean fuel technology will stay well ahead of petrol and diesel.

But Lang told the Power Supply Infrastructure for Alternative Fuel Vehicles conference in London: 'The pace of development of petrol and diesel fuels and engines is such as to suggest that gaseous alternatives may have missed their chance to be adopted on the grounds of significant environmental benefit.' He admitted that alternative fuels may provide a good solution for depot-based fleets, particularly because of their price, about half that of petrol or diesel, but for the rest of the fleet industry, and importantly, private users who will form the used market for such vehicles, he felt there were few benefits.

His concern was backed by Eastlake, who has carried out detailed emissions studies at Millbrook. He said: 'Bi-fuel vehicles may be eliminated because of the compromises on emissions they have to make. There is no detail on how tight new emissions limits will be in the next five years, but they could become so low that bi-fuel vehicles could no longer cope.'

The comments immediately drew fire from delegates at the conference, who argued that a 90% reduction in some emissions from alternative fuels secured them a long-term place in fleets. Heading the defence was Vauxhall, which has the largest range of dual-fuel LPG/petrol vehicles in the UK and will add to the range when it reveals a bi-fuel LPG/petrol Zafira at the London Motor Show in October. Malcolm Noyle, manager of alternative fuel vehicles for Vauxhall, said: 'While petrol and diesel technology is getting better, so is LPG. We have had 100 years to work on petrol and diesel and just a few years to work on LPG.'