Most other car makers agree.

Judging by the prototype Zafira, GM is at about the same stage of development with fuel cells as DaimlerChrysler and Honda, both of which have allowed limited test drives of research vehicles.

The fuel cell is coming - though there is no consensus on when there will be a viable volume production model.

At a presentation on the work of GM's Global Alternative Propulsion Center, the emphasis was shifted from fuel cell technology to a plea for the introduction of "the hydrogen economy".

Accidentally, the timing was perfect. The presentation was on the same day as the publication of a report by the Royal Commission on environmental pollution that warned of the catastrophic effects of carbon dioxide build-up and climate change. The report called for drastic action to cut down on the use of fossil fuels.

A fuel cell car is a pure electric vehicle that does not need storage batteries because the electricity is generated on-board by a catalytic process that combines hydrogen and oxygen gases. Water vapour is its only exhaust emission. The oxygen comes from the air but hydrogen - nature's lightest element - is more difficult to handle.

Because there are no hydrogen refuelling facilities, most manufacturers working on fuel cells have concluded that the hydrogen would have to be extracted by an on-board reformer from methanol, an alcohol that can be made from renewable resources and distributed and pumped in much the same way as petrol.

GM does not want to follow that route. It accepts that it may be necessary to have a system of extracting hydrogen from petrol (much more complicated than methanol) as an interim measure. But it is driving forward the idea of pure hydrogen being available at roadside filling stations.

Discussions are taking place with oil companies. They are sceptical but recognise that there are other chemical companies that could provide hydrogen - and that it could be generated at the filling station itself.

If there was a large investment in infrastructure, cars with conventional internal combustion engines could move to hydrogen fuel.

Some governments are taking an interest. Iceland intends to use hydrogen for all its energy requirements, and the natural gas pipeline from Siberia to Japan is designed to transport hydrogen.

There is also the question of how to store the hydrogen in the car. Ordinary gas cylinders of hydrogen are too bulky. The GM Zafira fuel cell car, named Hydrogen One, uses liquefied hydrogen that has to be maintained at -253ûC in a cryogenic tank like a big vacuum flask.

Absorbing hydrogen gas into a metal hydride or nano storage, in which hydrogen atoms attach themselves to minute carbon fibres, is also a possibility.

GM's alternative propulsion experts reckon that hydrogen should be in ready supply by 2020, by which time more than 20 per cent of vehicles on the road will be powered by fuel cells.

Such cars will be available long before then. Honda is promising to put a fuel cell vehicle on sale in 2003, and DaimlerChrysler and Ford - partners with fuel cell maker Ballard - predict a market introduction in 2004.

GM, which now has an association with Toyota for this kind of advanced research, would like to be more conservative but accepts that it may have to enter the race earlier if it is not to appear to be trailing in technology. Obviously it is not.

CAPTION: SO COOL: Hydrogen One uses liquefied hydrogen kept at -253ûC