Road Test: BMW 5 Series ActiveHybrid 5 4dr Step Auto

'Performance hybrid' looms large in the tag cloud these days, with Lexus and Porsche prominent. But they're mostly spoiled by clunky delays when you floor it, while their powertrains rearrange themselves from economy mode to power mode.

This BMW 5-Series is different. If you want performance, you have to apply in advance by rocking a switch, but then you get a good time all the time, until you deliberately switch back. So when there's some good road ahead, get into Sport mode, and the economising goes out the window. The engine-stop never happens. The eight-speed auto 'box favours high revs (or you can paddle it, and it answers alertly). The adaptive dampers take a more tensioned approach. You are in a proper BMW.

The hybrid is actually marginally quicker than a vanilla 535i, even though they share exactly the same 306bhp turbo straight-six. The extra pick-up comes because the hybrid e-motor is, in Sport, locked to the engine, acting as a booster when you boot the throttle and grubbing back charge only when you lift. But, that way, you're looking at 20-odd mpg.

So let's switch to Eco mode. Throttle response softens right off, and, wherever there's a chance, the engine declutches and shuts down, the car relying on forward momentum (decelerating or going downhill) or e-power (wafting at town speed). That process is smooth enough that you soon stop noticing, but treading only gingerly on the throttle can net you 35mpg, even as you keep up with most other traffic.

This new hybrid system is comparatively simple. The battery is behind the rear seats (ruling out a Touring). The automatic clutch is between the engine and the e-motor, which itself sits in place of the absent torque-converter, and does the same job on starting up. The eight-speed auto 'box is largely unaltered, reducing the price premium.

Intriguingly, this hybrid's price, performance and economy are all in line with a 535d. But the diesel can't glide this silently through town, nor act the rev-happy hoon when you cane it.