Profits at Johnson Matthey, the precious-metals company that makes catalytic converters for cars, could be as much as 15 per cent lower in the next six months as carmakers cut production.

The company's share price rose by 15 per cent to 832p on Wednesday as its prediction was better than expected.

Neil Carson, the chief executive of Johnson Matthey, said: “We are still going to get some growth this year, which is more than many businesses...attached to the car industry.”

He expected vehicle production to fall by 11 per cent around the world in the next six months as carmakers cut production, often by stopping their factories for months at a time.

Profit before tax at Johnson Matthey rose by 20 per cent to £144.9 million in the six months to September 30 as platinum rose to $2,250 an ounce. Prices have since fallen as low as $850 an ounce as investors have been forced to sell off platinum. A series of gloomy announcements about car production have also driven down prices.

Johnson Matthey is one of the largest distributors of platinum in the world and markets Anglo Platinum, the world's largest platinum producer. It said that profits from its platinum marketing and distribution business will be lower in the second half of 2008-09, compared with a “very strong result” a year earlier.

Mr Carson said that Johnson Matthey should benefit from new regulations on emissions that require vans in the US to have two catalysts from 2009. Diesel-fuelled cars made in the EU from 2010 will also be required to have catalysts to reduce emissions.

Platinum prices may be driven up again if some of the South African mines, which produce much of the world's platinum, are forced to close when prices fall too low, creating a supply shortfall.

Johnson Matthey believes that the price between now and May will be between $700 and $1,400 an ounce — a very large range. Research by Edison predicts an average platinum price of $1,350 an ounce in 2009.

Charles Stanley analysts said: “The results beat our and the market's expectations, which had naturally been lowered due to the group's exposure both to Platinum Group Metals and the global automotive sector. ”

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