Road Test: BMW X6 ActiveHybrid 5dr Auto

Don't bother looking  for the ActiveHybrid X6 in UK showrooms as it isn't ever going to appear here. The company reckons the two diesel and two petrol engine options it already offers in this niche-splitting car is more than enough already. And, truth be told, it's right.

Billed by BMW as the most powerful hybrid car in the world - a claim that's going to have several car makers reaching for their spec sheets - the impressively complicated but also quiet and swift ActiveHybrid X6 just wouldn't make any sense in the UK. Quite apart from the fact that this version will cost the same as the X6 M in the US, and over 40 per cent more when it hits European markets next year, it really doesn't do anything usefully better than the oil-burner, other than being a hybrid.

OK, it's appreciably quicker to 60mph, shaving almost three seconds off the 3.5-litre diesel's time. But it has the same top speed of 130mph, almost identical mid-range performance and appreciably worse fuel consumption. BMW reckons it will return an average of 28.5mpg, compared with 34.4mpg for the 3.5 diesel, but on our relatively sedate test route the X6 we drove knocked back a gallon of premium every 20 miles.

So why go to all this trouble to make such a car? Diesel-hating, hybrid-obsessed west coast America, that's why. In places like Los Angeles, where appearances are more important than sense or facts, and petrol costs less than two quid a gallon, the roads are clogged with Priuses and Lexuses. For these people the ActiveHybrid X6 will be the new must-have car. Because not only is it a hybrid and an SUV (of sorts), it's also got a massive V8 - every American's birthright - under the bonnet.

It's the same 400bhp twin-turbocharged 4.4-litre lump that powers the 5.0 petrol X6, but with the hybrid technology stacked on top of it; there's so much new stuff they had to make an extra bulge in the bonnet to accommodate it all. Then there are a couple of electric motors in the gearbox, one for high speed the other for low-speed assistance, which produce 91bhp and 86bhp apiece. They also capture energy generated while braking and send it back to the 2.4 kWh nickel metal hydride battery that sits in the spare-wheel well.

The battery is quite a small unit, but it still allows the car to be driven in all-electric mode up to 37mph. The only problem is that it runs out of charge after 1.4miles, so it's all about boosting rather than replacing the petrol engine's efforts. Efforts which, smooth and seamless as they are, are not better than a simpler, cheaper, lighter, more economical diesel.