Other 4x4 manufacturers have shown that making a vehicle of this ilk go fast is not the work of a genius. Speed with control has proved beyond most of them though, and BMW's X5 4.8i M Sport has the handling to match its 355bhp shove. Socially reprehensible, maybe, but huge fun nevertheless.

Before the original BMW X5 came along, big four-wheel drives tended to know their place. Yes, there were cranky one-offs like the Lamborghini LM002 and various Overfinch-tuned Range Rovers that plumbed powerful engines into big sports utility vehicles, but all too often this surfeit of horsepower only served to highlight the shortcomings of a chassis derived from basic agricultural equipment. The X5 changed all that. Some initially sniffy comments that it was little more than a 5 Series Touring on stilts were meant as a barb but merely highlighted quite how good the X5 was to drive. So much so that 90 per cent of all X5s sold were specified in more focused Sport trim.

The market for these vehicles has developed significantly in the eight years since the first X5 appeared. No longer is there any real requirement to pretend that the sportier models will go off road. BMW has finally taken the X5 off the leash and given us the 4.8i M Sport.

The billboard figures behind the X5 4.8i M Sport are the 355bhp the engine generates and the 0-60mph sprint of just 6.2 seconds. Yes, that makes this behemoth Beemer almost as quick off the mark as a Porsche Cayman but the straight line speed is only a small part of the X5's dynamic make up. BMW's intent is obvious when examining the finer engineering beneath this car. Instead of a high-mounted engine that stays clear of water, much as you'd get in most 4x4s, BMW has gone the opposite way, mounting the engine and gearbox as low and as far back as possible for an aggressive centre of gravity to help spirited cornering.

"A tiny piece of such wonderfully errant madness brightens most right-thinking people's day."

As well as intelligent xDrive four-wheel drive, the X5 ushers in Adaptive Drive and Active Steering for the first time on a BMW X model. Adaptive Drive uses active hydraulic anti-roll bars to counteract the cornering forces of the car to keep the body from leaning too heavily and unsettling the occupants. In addition to this, Adaptive Drive incorporates an Electronic Damper Control system that uses sensors to continuously adjust the damper setting for optimum comfort. Active Steering uses an electronically operated planetary gear intersecting the steering shaft that adds more lock than that dialled in by the driver at slow speeds to make parking easier. When driving at speed the opposite occurs, offering extra reassurance and more dynamic feedback. Capable of a top speed of 150mph thanks to an engine that develops 475Nm of torque, driving at speed is a given in the 4.8i M Sport.

Let's have a look at the pertinent facts. This X5 is only 19cm longer than the old model but manages to incorporate up to three rows of seats. Even with all three rows occupied, there's still 200 litres of boot space. In a more conventional five-seat configuration, the X5's boot measures 620-litres, up 155 litres on its predecessor. There's also an additional 90-litre storage compartment under the floor if you're not interested in having seven seat capacity and BMW reckons that only around 10 to 15 per cent of buyers will opt for the extra seats. This X5 is also 6cm wider than its forebear but, in another case of the engineers pulling a rabbit out of their hat, weighs no more in base specification.

The styling of the car is a good deal more conservative than many contemporary BMWs with little of the ostentatious 'flame-surfacing' seen on models such as the 5 Series and Z4. Instead, BMW has adopted a more restrained look and feel that lifts the best aspects of modern BMW design language and fuses them together in a broadly harmonious fashion. The dashboard features the same 'wing' design as many BMW saloons while the stance of the car is much like a supersized and rather chunkier X3. It's a very deft piece of styling that, in common with its predecessor, manages to disguise its bulk superbly.

The 4.8i M Sport sits close to the road thanks to the combination of its sports suspension and M Aerodynamic body styling package. Elsewhere there are 19-inch V-spoke M alloy wheels, a matte aluminium trim for the side windows, Shadowline roof rails, and a choice of six colours, two blacks, plus a white, blue, grey and silver. The interior features the trademark M Sport anthracite head lining, an M leather-finished steering wheel and sports seats. It's predicted that most customers will also opt for the bigger 20-inch alloy rims.

Given the car's equipment and capability, the £53,440 asking price doesn't seem that exorbitant. The three super-heavyweights in this class cost a good deal more and are only fractionally quicker. The Porsche Cayenne Turbo won't leave you any change from £75,000 and the Mercedes ML63 AMG and the Range Rover Supercharged Vogue SE are much the same price. Therefore the BMW slots between these leviathans and other big punchers like the £40,000 Jeep Grand Cherokee SRT8. It could well prove a lucrative niche.

No vehicle this big with a 355bhp petrol engine is going to be markedly inexpensive to run and the BMW doesn't pull any rabbits out of the hat in this regard. Fuel economy is quoted at 22.6mpg on the combined cycle but if you could extract much more than 16mpg on an everyday basis I'd be astonished. BMW also makes some play of the fact that at 299g/km, this X5 is a more responsible citizen than equivalent Porsche and Audi models but it's still a long way from a Prius. Latterly carbon dioxide figures have become more of a way of keeping score as to how advanced an engine is; spawning a constant game of one-upmanship between manufacturers. Perhaps that's no bad thing.

Insurance is rated at a tip-top Group 20 and residual values are rather held hostage to knee-jerk legislation. Big 4x4s like this are in danger of becoming a political punch bag. Chances are that typical owners may well have the funds to stomach those costs but used buyers could well be a little bit more wary.

There is very little logical reason for the existence of a vehicle like the BMW X5 4.8i M Sport. This fact is at once its damning epitaph but also, rather oddly, its saving grace. Because this vehicle is a plaything, a rather self-indulgent bit of fun, its sales in absolute numbers will be tiny. In other words, it's not worth getting in too much of a stew over from an environmental perspective. Lobbying television manufacturers to get rid of standby modes would be a far more productive way of venting your green spleen.

Admire the X5 4.8i M Sport as a very impressive piece of engineering that does its best to stand the laws of physics on their heads and you'll come round to its way of thinking. There's enough buttoned-down rectitude in the world already. A tiny piece of such wonderfully errant madness brightens most right-thinking people's day.

TOP 3 X5 DEALS

The results below show the top X5 deals on buyacar

	BMW X5 3.0d M Sport 5dr Auto Off Road
	ETR	Mthly	Saving	Price £46,486
	BMW X5 4.8i M Sport 5dr Auto Off Road
	ETR	Mthly	Saving	Price £54,933
	BMW X5 3.0si M Sport 5dr Auto Off Road
	ETR	Mthly	Saving	Price £46,128