IAN is revving up a shiny blue Jialing motorbike — the brand of choice for weaving between the traffic on Shanghai’s clogged thoroughfares.

Thousands of miles from home, it won’t be travelling much further. Bolted on to a bracket, the bike’s engine turns over smoothly as it sits in a warehouse in Hertfordshire opposite a silver Zafira, two black VW Golfs and, in pride of place, a Bentley Continental convertible.

Round the corner, a cream four-wheel-drive Saab is being put through its paces by a robot driver in a fridge cooled to precisely -20C.

This is no ordinary car park. Models from across the world have been gathered together for a single reason — to advance the expertise of Johnson Matthey, an unsung star of British manufacturing that has quietly made itself a key supplier to the global automotive industry.

For all these vehicles, the clue to Johnson’s business is at the back. Tight around the exhaust is a 2ft red rubber pipe that can be plugged into a steel tube to measure its emissions when the engine has been fired up.

Right now, Ian’s Jialing is being tested. A fan blows into his face to simulate the wind of a road trip. A computer screen guides him through the gear changes to mimic a regulation drive.

“It’s not about drag, it’s about cooling,” he said, as he checked the bike’s catalytic converter, which uses unburnt fuel to cool engines when they reach 1,000C, reducing their efficiency.

Johnson was once the Bank of England’s assayer of gold. Since California’s Clean Air Act of 1975, it has adopted a green lustre that propelled it into the FTSE 100 in 2002 and has driven its shares up 172% in five years, giving it a market value of more than £4 billion today.

From its headquarters in leafy Royston, a short drive from Cambridge, it has developed the technology that supplies one in three new cars worldwide with a catalytic converter.

As clean-air legislation has spread around the world so has Johnson’s business. Last year it supplied 23m vehicles with a converter, a honeycombed ceramic cylinder doused in chemicals “canned” in a car’s exhaust apparatus. As further laws are introduced — notably a legal requirement for diesel cars in Europe to be fitted with a soot filter by 2010 — its market is growing.

“The drivers for our business have never been better really,” said chief executive Neil Carson, no pun intended.

Taken together, its environmental-technologies division accounts for two-thirds of revenues, once the sale of platinum has been stripped out. Group pre-tax profits rose 16% to £262.3m last year. Earnings growth, which has averaged 8%-10% in recent years, is predicted to hit 14% in 2009.

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