THERE'S not much visually to mark out the 155mph Audi SQ5 as something rather special.

If you miss those four rampant exhausts pipes, there are just spoilers and a few badges to give the game away that the upright SUV has a twin-turbo V6 diesel that sends it to 62mph in less than six seconds.

That's quicker than a Porsche Cayenne and swifter than most sports cars. Audi, perhaps surprisingly, chose diesel power for its first ‘S' version of an SUV.

The formula works brilliantly because as well as providing the mid-sized Q5 with oodles of torque - ideal for fast cross-country travel or motorway overtaking - it acquits itself well in terms of economy and CO2 emissions.

Obviously the practical nature of the model remains unaffected by the transplant which has boosted power by more than a third to 309bhp.

The extra horses are immediately noticeable and accompanied by a purposeful burble from exhaust.

Response is instantaneous as the eight-speed Tiptronic automatic gearbox flicks down the ratios to catapult the Audi forward. Steering wheel paddles allow you personal input, if you wish.

Progress is as effortless as it is relentless with a seamless band of acceleration and very little wind noise or mechanical commotion.

Despite being ‘lured' into some very rapid journey times, the SQ5's consumption in my hands never dropped beneath 25mpg and most of the time hovered around the 32mpg mark. CO2 emissions are an impressive 179g/km, making it a reasonable vehicle, considering the immense performance, for company car drivers to run.

Road holding and handling is much improved over the standard 3.0 Q5, with very little cornering roll and tenacious grip via the huge 20-inch wheels shod with low profile rubber. But don't expect too much involvement from the steering.

The steering remains unusually lifeless with little feedback from the road. Regular Audi drivers may regard this as the norm, but those more used to being behind the wheel of a Jaguar or Porsche may be left wanting.

A by-product of the roll-free cornering angles is the firm ride which borders on harshness and can become joggly over rippled surfaces. I experimented in altering the various suspension settings via the onboard computer but didn't manage to find anything suitably composed and absorbent.

With 540 litres of cargo space before you sling down the back seats, the SQ5 is big enough for most families. The tailgate is powered but reacts quickly enough, and the rear platform is set quite low so cargo is easily loaded.

The facia and cabin styling are pure Audi with high grade trim, plenty of soft-touch, classy plastic and quality leather seating. The dash, dominated by a central sat-nav screen, will be familiar to A4 drivers which is hardly a criticism.

Multi-zone climate control and xenon headlights are standard. Driving position, however, is more upright and higher, allowing improved road vision.