I have driven the future and it isn’t electric. Nor is it hydrogen. It’s a diesel hybrid. Citroën’s Hypnos is the first model to combine a diesel- burning engine with a battery-powered electric motor that recharges while the car is braking. Admittedly it is a prototype, but the company says the technology will be rolled out across its range by 2011.

In many ways the biggest question about this car is what took them so long? Hybrid technology has been around for more than a decade, and the most well-known hybrid car — the Toyota Prius — is now in its third generation while Honda has recently launched a new, improved version of its Insight. Both these cars combine an electric motor with a petrol engine, which is less efficient than a diesel.

So why has no one thought to make a diesel hybrid before? The answer has nothing to do with technology and everything to do with marketing. Both the Prius and the Insight sell most in North America and Japan, places

where you will drive for many miles before you see a diesel fuel pump. So it has fallen to a European car company to combine the two and create a hybrid that will boast a fuel economy and emissions level that previous hybrids aspired to but never achieved.

Citroën claims that the Hypnos, with a 2-litre diesel producing 200bhp and a further 50bhp from the electric motor, will have similar performance to a conventional 3-litre car, but will do 62.7mpg and emit less than 120g/km of CO2. Few 3-litre petrol engines manage even half that figure. Once Citroën starts rolling the technology out among its smaller-engined cars the figures will become even more impressive, it says.

The Hypnos differs from existing hybrids not just in the fuel it uses. Cars such as the Prius and the Insight blend the operation of the normal engine and electric motor through the same set of wheels. In the Hypnos, the diesel engine drives the front wheels while the electric motor powers those at the back. This not only has a pleasing (and cheap-to-produce) simplicity, it also has the benefit of providing four-wheel drive when needed. So when the Hypnos pulls away from rest, it does so in complete silence, driven by its rear wheels alone, and only once your speed rises above 15mph does the diesel kick in. That means if you’re cruising around town, great chunks of your journey can be completed in emissions-free silence.

So what is it like to drive? I’ve never sat in a functioning concept car that was anything other than rubbish when fired up, and this one is no different. On its massive 22in wheels the ride quality is somewhere between poor and atrocious. Its steering is as heavy as a submarine hatch, and in one half-hour slot it managed to break down twice.

Even so, there are some impressive touches that differentiate this hybrid from its petrol cousins. The first thing you notice is that because diesel engines tend to have more torque at low revs the car feels eager at the point at which the power source switches from the electric motor. In petrol hybrids there tends to be a delay while the engine builds up revs after the switchover. On the downside, with diesel engines being noisier than petrol units, the contrast between the silent battery power and the diesel engine is more pronounced.

More encouraging is that when this hybrid system goes on sale two years from now, under the bonnet of the yet-to-be-launched Citroën DS5, the flagship of the new DS range, it should improve its efficiency and performance further still. And if you like the idea but don’t want a Citroën, exactly the same system will be launched in a Peugeot 3008 (Citroën and Peugeot are sister companies) at approximately the same time. Rest assured, Europe’s other brands will be secretly working on diesel hybrids too.

Citroën also claims to be developing smaller hybrid engines that will work in two-wheel-drive vehicles such as the C3 and C4 and, within four years, in its ultra-frugal C-Cactus car, which will sip fuel at a rate of better than 85mpg.

The Hypnos also offers some clue as to the direction of future design for the company. It won the concept car of the year award when it was unveiled at the Paris motor show last year and it’s clear that Citroën has pulled out all the stops in an effort to inject visual flair into its design.

Coy as car manufacturers usually are when talking about their concept cars, its cost is quoted only as “millions of euros” and its job is “to jolt the world into thinking about Citroën as the style and engineering leader of the mainstream European car marques”.

And if that seems an unusually lofty aspiration for a car company better known for its worthy people-movers, bear in mind that 50 years ago no one blended design and technology better than Citroën. Back then, cars such as the Traction Avant and DS built a reputation upon which the car maker has dined out for decades.

The Hypnos certainly looks the part — a mesmeric assortment of curves, swoops and slots — but it is the engine technology that will truly set this car apart. And on that score, Citroën says it has only just begun. Further down the road to the future, lithium-ion batteries (such as those already used in the Tesla Roadster) will boost the amount of electrical power that can be stored onboard.

And by the time it arrives, the diesel hybrid is likely to have a plug-in facility so the batteries can be recharged from the mains as well as from electricity generated during driving.

This, then, is how technology advances. Not in huge, unfeasible leaps, but in refinements that, little by little, improve efficiency and make life easier.

Hot Wheels specs

Engine type 1997cc, four cylinders, plus electric motor

Power/Torque 200bhp @ 4000rpm / 306 lb ft @ 2000rpm plus 50bhp / 147 lb ft from electric motor

Transmission Six-speed paddle shift

Acceleration/Top speed 0-60mph: 9.4sec / 132mph

Price/Tax band Not available

On sale Never, but powertrain due in 2011

Verdict A fabulous look into the future