Price £57,609
MPG 34.4
Top speed 150mph

It's accepted that if you're the sort of sadistic motorist who enjoys giving Mother Nature a good thrashing, your first weapon of choice would be a 4x4. If you can't get your hands on a two-tonne off-roader then a Porsche would probably be your next best bet – all but two of its 56 models currently on sale in the UK are in Band G or higher for CO₂ emissions. The perfect tool for eager nature vandals would, of course, be a Porsche that's also a 4x4.

Some of you will be surprised to learn that Porsche, makers of beautifully balanced rear-engined sports cars, even make an off-roader. But the Cayenne has been a feature of our crowded roads since 2002 – a much-improved second-generation of the SUV was unleashed earlier this year. In the first four weeks it was on sale, more than 16,000 orders were received. In fact, the Cayenne is now the biggest-selling model in Porsche's history. How ironic that a lumbering SUV should be a sports-car manufacturer's most popular product.

Here's something else that'll surprise you. There's now an eco version of the Cayenne. So, we have a green Porsche that's an SUV… what next? A Porsche driver who isn't a bonus-wielding banker?

It's all a sharp turnaround from when the car was first launched. I can still remember the shock of seeing one of the bloated beasts in the flesh. Like the fat-faced love child of a 911 roadster and a bouncy castle, it was one of the ugliest cars I'd ever seen. But its overshot jaw and bulging panels have slowly grown less startling. Today, like the neighbours' snuffling pug, it has a certain jolie-laide appeal.

The latest Cayenne is lighter, more agile and more powerful than the outgoing one, which means that the S Hybrid somehow combines the sporting performance of an eight-cylinder engine with the economy of a six-cylinder and the drive is gutsy and powerful, yet as smooth as Kate Middleton's cheek thanks to a revolutionary eight-speed gearbox.

Like all hybrids, the Cayenne has two engines – a 3-litre V6 petrol unit which combines forces with a separate electric motor. Heat lost through braking is salvaged and stored in the car's huge batteries, from where it can be called upon to help push the Porsche along in an unexpectedly mild and serene manner. At a mere 193g of CO₂ per km and an excellent fuel consumption of 34.4mpg, the Hybrid is by far the cleanest Porsche in the company's portfolio. It's so clean, in fact, that it's congestion-charge exempt in central London. Again, how ironic that a 4x4 should be a manufacturer's cleanest product. At the end of each journey, the onboard computer reveals what percentage of the previous journey was emission free. Over a week, about 47% of my driving was as sweet-smelling as a baby's breath.

There's so much for Porsche to sing about, you'd think they'd be giving their two-tone horn a well-deserved blast. But rather than plastering the Hybrid with green badges so passersby are left in no doubt, the only indication is the word "hybrid" in chrome clinging apologetically to the Cayenne's mighty flank. After enduring decades of abuse, it seems, the last thing a Porker driver wants to be seen as is a snivelling eco-convert.

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Email Martin at martin.love@observer.co.uk or visit theguardian.com/profile/martinlove for all his reviews in one place