The black cab is being fitted with a hydrogen fuel-cell engine that Zevco, the British company responsible for it, claims can deal with many of the pollution problems that world governments are struggling to solve.
Various ventures are under way to find alternatives to the internal combustion engine. But Nick Abson, a former producer of television science programmes and director of Zevco, says he is ahead of the competition in coming up with something that can be manufactured rather than the perfect solution.
He is targeting the commercial market because he believes car makers will be reluctant to support a venture they have not created. And he is optimistic that the tour by the London taxi - which he sees as a powerful symbol - will convince taxi operators around the Continent to convert from diesel, paving the way for a successful UK launch at the end of July.
Mr Abson is confident that bus operators will also see the appeal. He is working with Robert Wright & Co, Britain's principal builder of buses, with the aim of having one operational by the end of the year.
Mr Abson believes the time is right because not only is concern about the environmental effects of vehicle emissions escalating, but privatisation has given UK bus companies a commercial imperative. One attraction is that because the engine's only emission is water vapour, buses running on the fuel cells, made of thin layers of plastic, will be exempt from emissions tests, so reducing servicing bills.
Moreover, the hydrogen used in the cells is cheaper than diesel. Mr Abson puts the cost of hydrogen for a typical London cab at pounds 6 a day compared with pounds 15 for diesel, though he thinks the cost of hydrogen will fall to pounds 2 a day when there are more vehicles using it and more supply points. He says just seven depots for hydrogen - which is "much more available than people think" - could serve all 17,000 taxis in London and other commercial vehicles such as Post Office vans.
Ultimately, he hopes that taxis, buses and other commercial vehicles will be fitted with the engines when they are built. But even with conversion costs of more than pounds 2,000, he claims there will still be advantages in terms of cost and other benefits over the full lifetime of the vehicle. "The engine is silent, and there's no vibration," he says.
Although the top speed will be slightly lower than standard taxis, performance in normal conditions is broadly similar.
Though Zevco is a British concern - it is completing a pounds 2m manufacturing facility in Ramsgate, Kent - the technology was developed in Belgium for the European space programme. When this slowed Elenco, the company behind the fuel cell, was left without an application.
But Mr Abson, who was prompted to leave television by seeing a lot of science being wasted and by a growing concern for the environment, saw the technology's potential as a clean fuel. For a nominal sum he bought the company, which had swallowed pounds 30m of investment, and set about developing the cells for commercial use.
If he succeeds, it will be a genuine triumph of the little man over the big corporation. Mr Abson is pitting himself against ventures involving some of the world's biggest automotive companies and other big names. Backing him are 60 investors who have stumped up between pounds 1,000 and pounds 500,000 each to produce a pounds 1m war-chest. "They are highly significant and courageous," he says.
Mr Abson is convinced that urgent action is needed on the environment if gradual decline is not to turn into sharp deterioration. He says his mission has been made difficult by general indifference, particularly in the UK. He feels governments have been slow to support him as they do not understand the technology and worry about losing fuel tax revenues.
But he has found the new Labour government more responsive than its predecessor, he says. "It's been extraordinarily difficult. But we're nearing a considerable success."Reuse content