Audi's new SQ5 may be the first diesel and sport utility in the performance S range but it works says Matt Kimberley, PA motoring writer.

I know what you're thinking. Diesel? An Audi S model? Are you mad? Something along those lines would be about right, I'm betting.

But they said the same thing about putting a man on the moon, and while nobody's suggesting the SQ5 represents something quite that bold, putting a diesel V6 into an Audi S model has raised eyebrows.

The truth is that there's never been an S-branded Audi sport utility vehicle, and since no SUV can ever really hit the heights as a proper driver's car simply because the physics of their size and weight won't allow it, the normal rules of S-dom don't apply.

The SQ5 is the range-topping Q5. It's the fastest, the most advanced and the only one to be fitted with the astonishingly good 313PS twin-turbo (BiTurbo in Audi speak) six-cylinder diesel. Not that it sounds like a diesel when it's moving, thanks to a 'sound actuator' in the exhaust that translates the organic engine noise into a surprisingly V8-like grumble.

The car looks fabulous. In dark blue the SQ5 has an ever-so-slightly overstated presence. It's not too brash – it just looks ideally proportioned, muscular and, well, expensive.

Ultimately a diesel makes more sense for this car – a petrol engine would work, but it'd be incredibly thirsty. The BiTurbo claims more than 41mpg, and fuel economy is something few people can afford to ignore these days, if only just to avoid any risk of negative PR or sales flops. Only very low volume cars can still afford to be, as the Americans would say, gas-guzzlers.

But while the extra weight blunts the big TDI's throttle response a little, it's still unrealistically quick, passing 62mph in 5.1 seconds on the way to a limited 155mph top speed. For something as relatively heavy and aerodynamically inept as the Q5, even a slightly lowered one, that's amazing.

So it's plenty fast enough to do the S badge proud and that's one major box ticked. Huge mid-range torque and a wonderful willingness to rev, pulling hard all the way up to just under 5,000rpm make its performance genuinely enjoyable to use. Fortunately the brakes are among the strongest you're likely to find on a road car.

The next major box it ticks is the interior, but previous recent Audi owners won't have doubted that for a minute. The materials are lovely – like the slices of layered wood and metal that serve as trim inlays. The unvarnished, black-stained wood and silver metal add a sort of pin-stripe style, even if the bare wood is vulnerable to knocks.

The leather is marvellous throughout and the general feel is of one of the most deliciously but subtly aggressive in any current Audi. Even the gear lever controlling the eight-speed gearbox is designed to mimic a manual shifter, and it's all very… cool.

There are negatives, like the lack of steering feedback and the system's variable weighting that can sometimes seem a little uncertain and inconsistent. It's also a big old thing, so despite the huge grip on offer from wide tyres, physics has the last word. That said, it's very impressive for its size and bulk.

Despite big, big performance and a beautiful interior, this is still a practical SUV if you're careful with the leather. The rear seats offer plenty of leg and shoulder room, there's a neat MP3 player pocket in the glove box and the boot floor is expansive, albeit high up because of the space taken up beneath it by the four-wheel-drive system.

It rides well enough given its stiffened suspension and 20in wheels, but upgrading to the 21in options might be too much with Britain's not so smooth roads.

The amount of technology is a bit of a Marmite factor. The depth of settings available is mind-boggling, and some people will find it infuriating. On the other hand, the gadgets and options are endless and some people will love it.

Internet connectivity allows access to handy live features like traffic updates, so you can see where the most congested routes are and work round them. It's a brilliant system that, if enough cars adopt it, will help use the available road network capacity better and reduce jams.

The two biggest memories the SQ5 leaves you with are firstly its huge acceleration, that sense of irresistible momentum, and after that how uniquely satisfying the interior is, in both style and quality. Arguably those are the two things that large S-branded Audis have been most known and appreciated for over the last 10 years or so. The SQ5 works, whether you believe it or not.