Car companies often announce some new tech for class-leading performance, economy, safety or tea-making ability. But then they quietly add it won't go on sale for another two or three years. Then, by the time you actually can buy it, some other maker has already got it beat.
Well, three years after they announced it, here's the Hybrid4: a diesel and flappy-paddle with FWD, but the engine also running a generator, feeding a small boot battery and an electric motor for the back wheels. Now it's available to buy, the DS5 Hybrid4's 99g/km (at least on the smaller 17-inch wheels, which you also owe it to your spine to choose) is no longer absolutely unbelievable. But it's still ruddy good.
It's not just about economy. In Sport mode, the diesel and electric parts go shoulder-to-shoulder for 200bhp. Oh, and because the e-motor is at the rear, you get four-wheel drive. The electric motor is too small to make it feel anything other than front-driven normally, but it will critically improve snow traction. Another huge benefit: in ‘hybrid' mode, swimming among suburban traffic, the engine is often switched off (in my test, more than half the time), so you glide along by e-power. It's very serene.
Economy? Great in town. Citroen says it'll save 30 per cent there, and 10 per cent on the highway. I drove it on a commuter route where my Peugeot 508 (a similarly large, fast diesel auto, but of conventional tech) would have got about 36mpg; the DS5 got 46. And, as I say, it felt quiet and smooth. When a gap opened, the acceleration was as torquey and brisk as advertised.
There are hesitations when you floor it, mind; it's not as well integrated as a single power source, and the single-clutch, semi-auto gearbox jerks shifts under full power. In light acceleration, the rear motor's pulse of torque is enough to smooth the shift pleasingly.
But remember, if you drive a company car, it lets you have a DS5, one of the very most enchantingly designed cars on the road and pay tiny benefit-in-kind tax. Genius.
1997cc, 4cyl/e-motor, 4WD, 200bhp, 332lb ft, 74.3mpg, 99g/km CO2, 0-62 in 8.6secs, 132mph, 1710kg
Expensive, but cheap tax - especially business tax - offsets it. If you're buying privately, get the plain diesel or the petrol