Buy with confidence. Buy a Mercedes-Benz S-class. That's always been the way; with Mercedes' top model range you knew you were getting the best. You could relax. No worries about temperamental electrical systems, built-in obsolescence or an excessive bling factor.

The S-class stood, rock-like and permanent, in a world of fleeting fashions, ready to massage its owner's ego and cosset its owner's physical being. No wonder Third World dictators would buy nothing else. No wonder it's the world's best-selling luxury car.

That permanence is important. There have been various S-class models over the years but, unlike with others, the arrival of a new model hasn't rendered the previous one passé.

They don't get old, they mature, and now there's an all-new S-class, just as the last one, launched in 1998, seemed to be getting into its stride - it was an understatedly handsome car. Gravitas and discretion in one confident package; it was the epitome of the boss Benz. What happened?

The new car - Mercedes calls it W221 - has gone all mortal on us, adopted the clothing of a transient. Those vast wheel-arch bubbles are just too flashy for an S-class. Embarrassing, but it will be in South African showrooms early in February, 2006 and those in the UK in December with prices ranging from about £51 000 (R586 000) to £99 500 (R1.14-million).

Then there's the boot lid, kind of Maybach-meets-BMW 7 Series in the way it sits on, rather than in, the body. It's mould-breaking and attention-grabbing but that's not how an S-class should be. It should rise above that sort of sensationalism, above the sudden sense of uneasy flamboyance that has swept all recent new Mercedes.

It works for the radical CLS four-door semi-coupé, whose roofline the S-class echoes, but it's not quite right here.

That said, the new S-class is more of a looker than its boxy ancestors of the mid-1960's and 1970's. Maybe it's trying to regain a flavour of the 1959-68 "fintail" models. If that's the idea, the style solecisms are partly forgiven.

Besides, the new S-class has a good reason to draw attention to itself; it's one of the most technologically dense cars yet. It can work out exactly how hard your emergency stop has to be to minimise the likelihood of another car crashing into its tail. It does this with the same pair of radar beams - one long-range and low-definition, the other short-range and more focused - that also informs the "active" cruise control which automatically slows you if you come up quickly behind a car.

Normally, a brake-assist function simply applies the brakes as hard as possible if it senses that you are panic-braking, but this one adapts itself to what is really happening.

More technology (admittedly optional, like the last bit): meet Night View Assist. When you drive on dipped beam you can't see as far ahead but with NVA you can, by means of a screen where you'd expect the speedometer to be, its image provided by an infra-red beam and a camera concealed in the windscreen.

Another hi-res screen

So what happens to the speedometer? Normally, you see what looks like a standard-looking dial except that it's actually a facsimile created on a high-resolution screen. All new S-classes have that. Switch to NVA, though, and the infra-red image that occupies the speedo-space is underscored by a bar-graph speedo instead.

Now we move our eyes towards the Merc's middle, and see another hi-res screen. It contains, among other things, the usual sat-nav and stereo displays.

Just ahead of the central armrest is a large, round knob you can turn, press and prod in various directions, your hand supported on a padded rest that itself lifts up to reveal the carphone. Sounds suspiciously like BMW's iDrive to you? Yes, but, thanks to much better screen menus and nearby buttons to give direct access to oft-used functions, the "Comand controller" works very well.

You can even use it to alter the shape of your seat, by means of a 3D graphic that lets you select the part you want to pump up or deflate. There's also an optional massage function and "dynamic multi-contour" system that pumps up parts of the seat to support you better when accelerating, braking or cornering.

Related to this is part of the enhanced "Pre-Safe" system that pads out the right part of the seat in preparation for the collision the S-class's sensors divine that you're about to have. The ability to move seats to the best position, close windows and pre-tension the seat belts is carried over from the previous model.

Interior design

I could go on about the technology within the S-class: active damping for the air suspension, optional active springing to keep the body level, a floor pan pressed with random dimples to make it stronger and to damp out resonances…

But let's turn to the interior design, visually more satisfying than the exterior. Thin bright-metal strips underline the wood and, from behind, those strips emanates a gentle light at night (controllable on "Comand").

Most switches are metallic, there's a square, watch-like clock between the centre fascia vents and, in long-wheelbase S-classes, the rear seats recline (as they have done for years). This time, though, there's more room because the new S-class is markedly larger in all directions.

The scene is set, then, for a serene drive. But I wasn't prepared for just how serene it would be when I set off in an S500, the only model in the range to have an all-new engine. This V8, actually of 5461cc, delivers a rousing 290kW and propels the hefty Mercedes to 100km/h in 5.3 seconds, yet uses less fuel than its five-litre predecessor.

Other engines range from the S320 CDI V6 turbodiesel (replacing the old S-class's straight six, already seen in other models and destined to be the biggest seller) through the S350 V6 to the twin-turbo, V12 S600 with 390kW. This last engine has colossal torque (830Nm compared to the S500's 530), sufficient to hurl it to 100km/h in 4.5 seconds.

Casually muscular

Moving off is ultra-easy. The automatic transmission selector lever is on the steering column. There's no complicated pulling and guiding, unlike the superficially similar system in the 7 Series; this is an ergonomically transparent car. The transmission has seven forward gears and you can control them with buttons on the back of the steering wheel's spokes.

Not that there's much need of manual intervention, so casually muscular is the engine. You can hear its V8 woofle when it's roused, a woofle attenuated by slightly different phasing of each cylinder bank's valve timing to even out the exhaust pulses; but when you're cruising, the S500 is as silent a car as I have ever encountered.

It would be easy for the driver to feel cut off from the world in such a car, but there's a connection to be made if you want it. Such is the effectiveness of the Airmatic DC suspension that this behemoth of a car feels accurate when rushed through corners, the ample forces it generates all acting in the right direction, the steering weighted perfectly.

There's no heaving or lurching even when the suspension is set to its usual comfort mode. Switch to sport and the ride firms up but not to the point of destroying the S-class's ability to finish off what an unconscientious road-builder started.

This is a very impressive car, one that puts Mercedes-Benz back on top as the maker of the world's best real-world luxury cars. It has taken a battering recently for letting quality slip but this new S-class is proof of a fight back. - The Independent, London