Motoring: Stepping on the gas: Conversion to natural gas engines is accelerating, thanks to a London cabbie. Graham Coster reports

'I HAD that black smoke coming out the back of my cab once . . .' There's a new line for the London cabbie of the future - and here's a new question for The Knowledge: where can you fill up your cab with environmentally friendly natural gas? Answer: down the Old Kent Road now, and in a few months' time at the Richmond Road Taxi Centre underneath the railway arches in Hackney.

As we sit in Dov Reichmann's office, trains rumble and roar overhead, drowning out his account of how he has come to introduce the first gas-powered diesel taxi into service in London. A twinkly man in a dapper grey pinstripe, Mr Reichmann went into the cab trade more than 20 years ago. Now he runs a fleet of 200 taxis out of Hackney and is bidding to stop the 'black' in the cab's name being identified with the filthy cloud of its exhaust smoke. 'I'm not normally this excitable,' he says, 'but this is enormously exciting.'

Technology to convert petrol engines to run on compressed natural gas is not new; with no national network of filling stations offering gas, however, there has been little opportunity to capitalise on an alternative road fuel that emits about 70 per cent less carbon monoxide, 30 per cent less carbon dioxide, no lead and virtually no particulates - or what we'd call smoke and soot. But diesel engines have proved more difficult to convert.

The breakthrough Reichmann is taking advantage of is the development of a 'dual-fuel' system by which a vehicle can run on diesel or gas. Fill up with gas if you're near your depot; if you find yourself on a long fare where there are no gas refuelling facilities, put diesel in and run on that: a microprocessor in the engine will automatically switch from one fuel to the other. Cab drivers who have a problem with their diesel being pilfered will appreciate the impossibility of siphoning natural gas out of a tank - it just evaporates on contact with the air - while British Gas's price of pounds 1.60 a gallon undercuts the price of conventional fuel by about 40p. Next year, Reichmann - who holds world rights for the system's application to the Ford 425 engine, standard power unit for the Transit van and the London Metrocab - plans to convert 100 cabs.

Visions of wartime austerity, when petrol shortages led to cars tootling around pulling trailers of coal gas to power them, may suggest that the gas cab is a British invention. In fact, we are lagging behind the rest of the world. In the Swedish city of Gothenburg, a fleet of 20 gas-powered buses entered service this spring, and Volvo has sold more to Vienna and Adelaide. Italy has a quarter of a million natural gas vehicles able to refuel at 230 places, and fuel-duty incentives to encourage its use.

In New Zealand, 10 per cent of all road vehicles run on gas; in the United States, motor manufacturers such as Ford and Chrysler already offer production models with a gas- power specification, and between 2,000 and 3,000 new natural gas vehicles are coming on the roads every month. California has set ultra-low emission levels which all new road vehicles must meet by 1999: Chrysler claims the gas version of its Ram van - America's equivalent of our Ford Transit - is the only model beating those standards already, and by 60 per cent.

Over here, the AA now operates two gas-powered Transit patrol vans. From next April, in a Department of Transport project to find ways of reducing city-centre air pollution, six gas buses will be running in Southampton. 'If one is into these things,' muses Southampton Citybus's managing director Ian Phillips, 'the smell from a gas engine is a lot more fragrant than that from a diesel.' By the end of this year British Gas will have converted 300 of its vehicles to run on gas, with another 500 scheduled for next year, when the 10 gas filling stations it has already opened around the country will be joined by a further 12.

At British Gas's Natural Gas Vehicles division the marketing manager, Tom Gorman, drives a Ford Granada Scorpio converted for gas, and is trying a new trickle-charge, home-

refuelling unit that enables you to fill up overnight, via a compressor, straight from the mains. As for performance, Mr Gorman judges the difference from a petrol engine 'imperceptible'. When pushed, he concedes 'a marginal reduction in power when it's flat out, but also a marginally smoother ride'.

But wouldn't there be a fearful conflagration if he crashed? No, he says, no leakage from a ruptured fuel tank - gas escapes into the air - and if a hole in the gas cylinder comes into contact with a flame the gas will burn like a cigarette lighter. And, because gas is moved around its national grid by underground pipes, if we all filled up with gas we could take 10,000 petrol tankers off our roads.

Fred Parker of the Natural Gas Vehicles Association - a confederation of gas utility companies and motor manufacturers - postulates some 200,000 gas-powered vehicles in Britain by the end of the century, and perhaps nearer 500,000 if the fuel tax structure was altered to encourage the use of cleaner fuels - hardly a staggering proportion of the 27 million vehicles already on our roads. However, Tim Brown, information officer at the National Society for Clean Air, warns that methane, the staple constituent of natural gas, is itself a greenhouse gas and is more damaging in smaller quantities than the other main offender, carbon dioxide. With catalytic converters becoming standard, he says, we should see a drop in levels of carbon monoxide and nitrogen oxides in our atmosphere anyway - but a counterbalancing increase in carbon dioxide, which catalysts don't deal with. So with a move over to natural gas in cities, 'You'd see an improvement in local air quality, but there might still be a national concern over our overall emission of greenhouse gases'. Tom Gorman says no methane would escape at filling stations as the gas is pumped through a sealed system, and the decrease in carbon dioxide offsets an increase in methane.

Bear all this in mind in case the cab pulling over to pick you up from The Phantom of the Opera is number E9073 and has a big blue-

flame logo on its side. How about a starter for 10 for driver Sid Gilbey, along the lines of: 'So, what about this protocol on global warming we signed in Rio, then?'-

(Photograph omitted)