Citroen Berlingo

Called the Efficient-C, this oil-burning hybrid Berlingo improves economy and CO2 emissions by 30 per cent over a regular diesel car, and the drivetrain should appear in the next-generation C4 in a few years' time. It's the result of a collaborative British Government-funded project that includes PSA Peugeot Citroen, engine specialist Ricardo and electronics experts at QinetiQ.

The Efficient-C uses a 92bhp 1.6-litre HDi turbodiesel, an electric motor, lithium-ion batteries and a SensoDrive automated gearbox. It works in a similar way to most hybrids, with the electric motor powering the car at low speed and the diesel taking over as you go faster. Under braking, energy is stored by the batteries, while at a standstill, the engine switches off. The result is a claimed 75mpg combined and CO2 emissions of only 99g/km. In comparison, the Toyota Prius returns 65mpg and puts out 104g/km.

So what's the catch? Well, predictably, it's the cost. Citroen estimates that the diesel hybrid technology adds £3,000 to the price of a Berlingo, which is why a production version won't go on sale until 2010. By that time, it is hoped that the cost of the technology will have halved.