The Mercedes-AMG G 63 replaces the old supercharged G 55 as the most powerful, quickest and most expensive version of the venerable G-Class 4x4.

Joining the six-cylinder diesel G 350 Bluetec in a revamped G-Class range that boasts higher levels of luxury than ever inside, the G 63 is powered by AMG’s latest twin-turbocharged 5.5-litre V8, whose 563bhp and 561lb ft of torque are sufficient to propel this 2.5-tonne brick from 0-62mph in a startling 5.4sec.

The V8 is mated to an equally modern AMG Speedshift seven-speed automatic transmission with a stop-start function and a choice of three modes.

This powertrain means that while the G 63 is the quickest G-Class in its history, it is also more economical than its thirsty predecessor and emits less CO2 – although figures of 20.5mpg combined and 322g/km hardly qualify the G 63 as being eco-friendly.

Most of the switchgear is familiar Mercedes fare, too – the exceptions being the trio of diff lock buttons high up on the centre console and a low-range selector button lower down. The lofty driving position is quite upright, but it’s very comfortable and roomy up front.

That comfort continues when the car is rolling. Despite its old-school rigid axles, the G 63’s ride is compliant and reasonably well controlled and refinement is commendable for this type of vehicle.

There’s a fair bit of body roll in corners and the quaint old recirculating ball steering is low-geared enough to keep the driver quite busy at times, but in general the G 63 is better mannered than you might expect, albeit no Porsche Cayenne or Bentley Bentayga.

One source of noise that is always welcome, of course, is that big twin-turbo V8 and the bellow that emerges from the naughty side-exit exhausts whenever you stir the throttle.

Once you’ve overcome a moment of initial inertia, the G 63 accelerates with the same inexorable force as a Bentley. Put it this way: its swollen performance is more than adequate for a vehicle like this, and easily accessed. You can even change gears manually via paddle shifters if you want.