Price: £45,030
Top speed: 155mph 0-60mph 6.3 seconds
Consumption: 31.7mpg
CO2 emissions: 209g/km
Best for: discerning Americans
Also worth considering? BMW 5 Series estate, BMW X5, Mercedes R Class

Everybody knows what a BMW is. No other brand has been honed as carefully as this one. No other badge conveys as precisely as the blue and white quartered circle what the car that bears it stands for. But it wasn't always so. Back in the Fifties and Sixties, the company's range was much more diverse than it is today; there was the Isetta, for example, a bubble car based on an Italian design, and the 700, which was broadly comparable with the British Hillman Imp.

It's as well to approach the new 5 Series Gran Turismo with that broader, longer-term perspective of what a BMW can be, because this new car is quite unlike anything else the Bavarian manufacturer has made before. Like the Isetta, the 5 GT is in a sense, a bubble car. But while in the case of the Isetta, the word bubble refers to the car's large glass area and bulbous form, in the case of the Gran Turismo, it describes the overheated economic conditions that produced it. Car manufacturers are always doing this sort of thing – optimistically cooking up expensive super-cars and niche products in the good times that then end up being launched during a slump.

The GT is such a niche car; it is aimed at those buyers who find a saloon or estate such as a BMW 5 Series impractical but who don't want to be seen in a big SUV like BMW's X5. I thought Mercedes had already proved this niche didn't exist with its R Class crossover but the 5 GT turns out to be rather different to the Merc. It's a commodious hatchback that puts a lot of emphasis on the comfort of rear-seat passengers, which puts it quite close in concept, if not in terms of execution, to the now defunct Vauxhall Signum.

And that execution is superb. From its beautiful cabin to its slick eight-speed gearbox, the GT is an immensely polished and practical product; it's just that it's not very sporty and it doesn't look like it should be carrying a BMW badge, a feeling that not even the marvellously powerful straight-six engine fitted to the 535i variant I tested can dispel.

Will the 5 GT succeed? Good as it is, I'm not sure how many Europeans will buy one. But I suspect that the Americans, who like something big and practical, and are far less impressed than we are by fussy notions of what premium brands stand for, could develop quite an appetite for it.

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