Mercedes’ 25-year-old Defender rival, the G-class, will finally be pensioned off in around a year.

And the big news is that its replacement will return to UK showrooms after a decade-long absence.

The all-new G-class will be a completely different proposition to today’s: luxurious as well as tough. The G is a jacked up, SUV version of the seven-seat R-class, set for an unveiling at Detroit next month.

Underpinning both cars – and the next M-class – is a monocoque chassis, promising a quantum leap in refinement and road manners compared with today’s ladder frame. But the G-class remains a serious off-roader. A clever air suspension is capable of raising or lowering the front or rear ends to minimise lean. Meanwhile, locking centre and rear diffs, low range and detachable anti-roll bars aim to make mud-plugging straightforward.

In addition, the family adopts Merc’s 4ETS four-wheel drive system. If slip is detected, it shifts torque to the rubber with the best traction and brakes individual wheels. The Merc also has a system similar to Land Rover’s Hill Descent Control, which repeatedly applies the brakes for controlled descents off-road.

Key hard points are shared with the R-class, including windscreen, door frames and the 3,125mm-long wheelbase. But the sheet metal differs.

The G-class gets a modern, pumped up look far removed from today’s box on wheels. Check out the sportier profile, beefy wheelarches and evidence of Mercedes’ accent line along the side. Up front, tall, geometric headlamps replace today’s circular lamps.

Overall, the G-class will measure around 5,100m in length, about the same as an S-class. That’s 300mm longer than the forthcoming M-class. All three cars will be built at Mercedes-Benz’s Tuscaloosa plant in Alabama, USA.

The big SUV, weighing close to 2.5 tonnes, needs hefty engines. The base unit is the new 3.0-litre V6 common rail diesel, shown in the Vision R MPV.

The lump kicks out 218bhp and 376lb ft. A 4.0-litre V8 turbodiesel will yield around 300bhp. Up to three petrol V8s could be offered: a 326bhp 4.6, a 408bhp 5.5 V8 and a 6.3-litre AMG delivering 462bhp.

Seven seats will be standard, and the equipment list lengthy. Expect it to feature bi-xenon adaptive headlamps, a powered tailgate, cruise control with autopilot and a heated front screen. Indeed, the G-class is so luxurious, it needs two batteries: one to start it, the other to power all the gadgets.

Expect UK sales by mid-2006, with prices from around £40,000.

IT’S BIG

G-class is as long as an S-class, with a whopping 3125mm wheelbase. Inside, there’s room for seven seats.

PLATFORM

Four-wheel drive monocoque chassis shared with next-generation M-class and R-class crossover.

ENGINES

Merc plans two diesels: a 218bhp V6 and 300bhp V8. Three bent eights will be offered, spanning 326bhp to 462bhp