There may come a day when BMW 5-Series hybrids roam our land as Ford Fiestas do now, but in that perhaps unlikely event they won't be of quite the same sort as the one tested here.That's because the ActiveHybrid 5 uses the three-litre petrol engine from the 535i in combination with an electric motor, and it's the engine that dooms this car to non-speaking part status in the UK, dragging likely sales here down to only a few hundred each year.A diesel ActiveHybrid 5 would be much more popular round these parts, but in the words of a BMW fellow the business case for such a thing "doesn't add up at the moment". The number one market for a hybrid 5-Series is the US, which may account for as much as three-quarters of sales, and the Americans still prefer petrol engines, so that's that.The combined output of the two power sources is 340bhp, well above the 306bhp of the 535i, but the extra 150kg carried by the ActiveHybrid 5 cancels this out almost exactly. With eight-speed automatic transmission (standard on the hybrid, optional on the petrol-only model) the two cars share the same 0-62mph time of 5.9 seconds.The point, of course, is that the hybrid has much better official fuel economy and CO2 figures. If you stick with the standard 17" wheels - and there's more than one reason for doing that, as we'll see shortly - it manages 44.1mpg and 149g/km, while the best a 535i automatic can do is 37.2mpg and 177g/km.That's an £80 drop in annual Vehicle Excise Duty payments right there, to say nothing of the potential reduction in fuel costs. And the ActiveHybrid 5 does its best to improve economy in ways that won't show up on the EU test. Most intriguingly, if you're using the standard-fitment satellite navigation system and the car realises that a hilly section is coming up, will make a point of storing as much energy in the battery pack as possible.On a full charge, the ActiveHybrid 5 can go for up to 2.4 miles, and at speeds of up to 37mph, using battery power alone. And if you were driving along a motorway at as much as 100mph . . . not that you would be, of course . . . the very thought . . . but let's say you were, and you backed off the throttle for whatever reason, the car would go into battery-only mode then too, not firing up the engine until you pressed the pedal again.One price you pay for all this ecological soundness is reduced practicality because of the need to store all the extra parts. The electric motor has been cleverly integrated into the gearbox, so it has no impact on interior space, but the battery pack has had to be mounted in the boot because it won't fit anywhere else. Luggage capacity is therefore the lowest of any 5-Series at 375 litres, the norm for the saloon being 520 litres.That might not matter, depending on your lifestyle requirements. If those same requirements include charging around the countryside like a boy racer, this really isn't the car for you.It's certainly quick in a straight line, but what it does best is waft langorously. Even under full-throttle acceleration right up to 7000rpm the engine note never becomes more than a distant whirr, as if the car is trying to encourage you not to do that again. The major controls, particularly the steering, are very smooth, and invite you to drive in a similar manner.The suspension is also, as they say, set up for comfort rather than speed, and I'm sure that in its natural form the ActiveHybrid 5 rides beautifully. The one I drove, however, was fitted 18" wheels and low-profile run-flat tyres which add £1095 to the price and are unspeakably ghastly. They transmit an incredible amount of road noise, they reduce the ride quality to that of a Grand Prix car running over the kerbs at a chicane - hell, they even make the steering column rattle. Ridiculous things. Avoid them. Engine 2979cc, 6 cylinders plus electric motor Power 340bhp Transmission 8-speed automatic Fuel/CO2 44.1mpg / 149g/km Acceleration 0-62mph: 5.9 seconds Top speed 155mph Price £46,865 Details correct at publication date
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