Motoring review: Porsche Cayenne Diesel S

Price: £58,243
Engine capacity: 4.2-litre V8 turbo diesel
Power output (BJP @ rpm): 382 @ 3,750
Top speed (mph): 156
0-62mph (seconds): 5.7
Fuel economy (mpg): 34
CO2 emissions (g/km): 218

A few weeks ago I went on holiday to sunny Somerset in a Porsche. It wasn't an agile sports car though; it was a great, big Cayenne SUV. Porsche sells more of these beasts than 911 sports cars these days and since its launch in 2002 it has become the ultimate Chelsea Tractor. More bling than a Range Rover and less of a true off-roader, it is loved from Elmbridge to Alderley Edge. This is the new super-fast diesel model (it will hit 60mph in less than six seconds) and while it may be as fast as some of Porsche's two-seater hot rods,it's far more practical on the way to the holiday cottage with a gang of troublesome toddlers and a baby in tow.

It does beg the question of what exactly the average Chelsea Tractor owner wants from their wheels? Automotive executives seem to think they want a whippet-fast SUV. It's hard to fathom but, believe it or not, you are spoilt for choice if you want an off-roader than will rival a supercar off the start line. There's the Porsche Cayenne Turbo, the Range Rover Supercharged and the BMW X5 M Sport if petrol is your thing. And now there's the Cayenne Diesel S if you want a monstrously rapid oil burner to get down to Waitrose in Esher to pick up some basil.

They cost from £50k to £100k-plus and the Cayenne Diesel S is the most sensible of the lot. It's still silly fast – it will hit 156mph – and if you can find a stretch of road long enough to unleash the mighty V8 engine you'll soon have one of those oh-look-some-pee-came-out moments when you realise you're taking a 2.2-ton tank into a bend at a far too great speed. It's not cheap to run though; brimming the 100l tank will cost you close to £150. In theory, this gives you a 745-mile range but that's far from likely.

From the Cayenne Diesel S then one can only assume that the average Chelsea Tractor owner wants to cross Europe at colossal speed and at great expense, navigating occasional muddy obstacles with their three children in the back complete with a vast amount of supplies and a fleet of Bugaboo buggies in the huge boot.

There's also the luxury to be taken into account. Chelsea types want leather and lots of it. Apparently they also want lots of options and with Porsche that gets frighteningly expensive. The digital television and radio set in my test model will set you back £1,368. That's a pretty monstrous price for the privilege of putting your nephews in front of CBeebies outside the Co-op while their parents nip inside for some bread.

This does expose another contradiction in this car – it's great for loading up with kids (they love the view) but can you imagine what car seats do to the soft luxurious leather? And what about crushed biscuits trodden into the carpets? After 600 miles, three or four serious tantrums and several mushed bananas I couldn't apologise profusely enough when the polite chap from Porsche came to collect it. And that's this car all over. It's wonderful, fast, spacious and built with the precision and attention to detail only the Germans seem to have. But if I owned one I'd never let children sit in the back, never cross Europe in it and never take it off-roading.