D-day could be approaching for the diesel engine. The future is looking petrol-powered, at least in the medium term.

The diesel sales boom has been phenomenal. In 1999, diesel powered just 14% of all new cars bought by UK punters. Last year, the oilburner munched 33% of the market, some 835,334 registrations.

But the keeper and interrogator of UK registration figures, the Society of Motor Manufacturers and Traders, predicts diesel will not break the 1m mark. It believes the peak will occur at around 918,000 units.

“Diesel has almost reached the top of the curve,” said an SMMT insider. Why? The answer is simple: economics. Diesel engines cost more to make than petrol engines – and those costs are set to increase further, as car makers face the challenge of meeting tougher emissions regulations such as Euro V.

Carl-Peter Forster, GM Europe president, says that Opel takes a hit of up to €1500 on every CDTi diesel it sells. “Opel has caught up with rivals on diesel technology, but that was bad news for our profitability. Right now, the customer is not paying for the true cost of the diesel,” says Forster.

Carmakers are still negotiating with EU officials about the amount of nitrogen oxides and particulate matter that engines will be allowed to emit when the Euro V standard arrives in 2010.

Opel’s solution is to invest in petrol engine technology, with direct injection, variable valve timing and turbocharging helping to meet emissions standards and close the efficiency gap with the diesel.

But is Opel merely moaning because it got its sums wrong? Nope, another heavyweight predicts that the rising cost of diesel technology could force punters back into petrol cars. He’s Rinaldo Rinolfi, Fiat’s research boss, and his is an opinion not to take lightly: Rinolfi was the mastermind who created common rail diesel injection.

Fiat and Opel aren’t alone. Premium brands like BMW and Mercedes are also pledging to divert funds away from diesel to petrol technology, which they believe has unfulfilled potential on performance and efficiency.

Petrol could be the bridge to a zero emission future promised by fuel cell technology.