WHAT'S the best-selling Porsche these days? Probably not the iconic 911 with prices starting at £67,270. My money was on the versatile Boxster, which is the cheapest route to a new Porsche at £36,572, or its coupe-cousin the Cayman.

I was wrong. The best-selling Porsche is not a sports car at all. It's a two-tonne SUV. That's right, the Cayenne 4x4 is the most prolific Porsche in the world.

It's also the most pilloried Porsche by fans who can't bear the thought of Porsche building anything other than sports cars.

But I'll wager most the Cayenne's critics haven't driven one.

It may share some parts with the VW Touareg and the Audi Q7 but, believe me, the Cayenne is still a Porsche first and foremost.

The new one is significantly lighter than its porky predecessor. In fact, model-for-model it's about 10 per cent lighter, partly as a result of using more exotic materials like aluminium and magnesium, but also because the low-ratio gearbox has been ditched.

Yet, despite losing 550lbs, it's actually bigger and, therefore, roomier in the sumptuous cabin.

The crash diet also means that it goes, stops and steers much better than before – news that should prove worrying for the Cayenne's rivals because this was always the sportiest of SUVs.

Porsche has purposefully designed the Cayenne to look smaller – ostensibly a strange decision in the “bling, bling” world of premium SUVs where bigger is often, mistakenly, considered to be better – but that's what customers said they wanted.

Visually it looks more cohesive than before with muscular curves, a coupe-like reverse slant rear window line, door mounted mirrors and a face that's inspired by the 911 Carrera GT (honest).

As far as big sales in the UK go, you can forget fancy notions of the terrifying turbo (how can something so big travel so fast?) - it's the turbo-diesel that'll be rolling out of Porsche showrooms.

Given that a diesel was one of the last arrivals in the first generation Cayenne's lifespan it's no surprise to discover that the Audi-sourced V6 is carried over pretty much unchanged.

Performance is improved, however, thanks to the weight savings.

If you can come to terms with the idea of a diesel Porsche then you'll find that this one is a true driver's machine. It won't hold on to a Boxster or a Cayman on a B-road, but, in sport mode, it's indecently fast for a massive SUV.

In fact, the 450lb/ft of torque, makes it feel faster than the on-paper figures would suggest.

There's no waiting as the automatic decides which of its eight different gears to select, the huge pulling power means the Cayenne just goes when you tickle the accelerator. There's real surge from as little as 2,000 rpm and plenty of punch for overtaking slower traffic.

Even better, it squeezes 30 miles from a gallon of diesel and puts out just 195g/km of carbon dioxide – a remarkable figure for such a big car. To put that into context, the gargantuan Cayenne is kinder to the atmosphere than a seven-year-old 2.0-litre Mondeo or an early MINI Cooper S. Extraordinary.

It's quiet too, and conceals its girth better than any other large SUV, including the BMW X5 and the Range Rover Sport.

Mind you, hustling down the kind of tight, twisting, sinewy roads we have in the North-East, does sometimes feel as though you're strapped to a rocket-powered supertanker.

It's reassuring to know that the brakes are supremely powerful and easy to modulate.

The diesel starts at the £45,000 mark and for that kind of money you get an eight-speed auto 'box and automatic stop-start for even better fuel consumption in heavy traffic.

The cabin (based on that of the Panamera super-saloon) cocoons the driver and front passenger in luxury. The fascia is festooned with buttons for almost everything but all the controls are logically laid out. The traditional instruments are clear and easy to see at a glance.

Our test car was fitted with Porsche's Active Suspension Management system which, in sports mode, tightens the helm considerably for a more satisfying drive. It can't defy the laws of physics, but the Cayenne can deliver when you're in the mood.

If you're a long-time Porsche fan, there's no reason to be suspicious of the Cayenne.

After all, BMW showed the world that it was possible to make a high performance diesel car more than a decade ago.

Since then diesels have won Le Mans and the British Touring Car Championship.

The new Cayenne pulls off the difficult trick of being lighter, bigger and better to drive. It looks good and seats five adults in hedonistic levels of comfort.

And if the profits Porsche pockets from Cayenne sales go towards making cars like the 911 GT3 RS what's not to like?

PORSCHE CAYENNE 3.0d V6 Price: £45,256

SPEC CHECK: Engine: 2,967cc turbodiesel V6 Max power: 240 bhp @ 4,000 rpm Max torque: 405 ft/lb @ 2,000 – 2,250 rpm Max speed: 135 mph 0-62 mph: 7.8 secs Boot capacity: 670 litres CO2: 195g/km Equipment: Porsche Active Suspension, central locking, alarm, immobiliser, alloys, climate, cruise, rear parking sensors, leather seats, CD player.