The CLK is such a niche product, says Ross finlay

While they have four-headlamp styling similar to that of the E-class, the Mercedes CLK coupe and cabriolet are actually built on the C-class platform. They are among the cars in its range which Mercedes admits are niche products, but the CLK, together with the SLK roadster, the V-class MPV, the modified AMG saloons and estates, accounted for more than 3000 UK sales last year.

Priced from #26,640, the coupe comes with either a two-litre 136bhp engine which is barely man enough for the job, the 193bhp 2.3-litre supercharged Kompressor unit, or the V6, with its 3.2-litre capacity and 218bhp. Newly introduced, the convertible offers only the Kompressor engine at #36,090 and the V6 at #41,140.

The coupe and convertible I tried both happened to be of the Kompressor persuasion. This is an engine about which several of my colleagues are anything but enthusiastic, largely on the grounds that it is a four-cylinder when what they really want in a Mercedes is a ''six'', and that it does not make any of the right noises.

But with a longer memory, which goes back to some screaming supercharged sports cars in hill climbs and race meetings in the fifties, not to mention the banshee howl of the V16 BRM, I am intrigued by any more refined ''blown'' engine of modern design.

As well as that, the steady boost of a supercharger is always there rather than arriving suddenly as with the familiar turbo. When you floor the throttle in a car like a supercharged CLK, there is a seamless increase in power.

The five-speed Kompressor automatic coupe gets to 60mph in just over eight seconds, goes on to a test track maximum around 143mph, has a likely overall fuel consumption around 28mpg, but is notably more economical than many of its rivals at steady cruising speeds.

Being substantially heavier, because of the extra strengthening built in to keep the basic structure as rigid as possible when it lacks a steel roof, and also because of the hood-operating mechanism, the cabriolet is slower all round and, model for model, less economical.

Mercedes has put plenty of fresh technical features into the CLK. It comes with a security system in which the ignition ''key'' is an electronic component rather than one of metal. Brake Assist is also standard, that Mercedes-patented system which boosts the brake pedal power in an emergency stop. Its early problems seem to have been solved.

Introduced with the CLK, the new Active Service System includes a sensor which calculates an individual servicing plan for each individual engine, depending on how hard the car is being driven, and in what conditions. A read-out display advises exactly at what mileage an oil change is due.

Out on the road, the coupe was a fine long distance car. It wafted through a long motorway journey at a very relaxed gait, although the supercharged engine responds quickly to throttle movements when necessary.

Mercedes seats tend to be on the hard side, and off the motorway I would have liked to feel more side support when driving the car quickly on more sporting roads. While I often find the Mercedes zigzag gear selector pattern rather fiddly, I enjoy using it manually for holding lower gears. The latest system is quite handy for this, because one snick sideways moves it from fifth to fourth-gear hold.

The cabriolet showed that the extra weight does slightly blunt its performance, although I expect that hardly matters to this model's typical ''lifestyle'' buyers. On normal roads, even taken at speed, I thought body rigidity was pretty good. It was only occasionally, over a really lumpy and at one place potholed surface, that any scuttle shake made itself apparent.

German convertibles used to be notorious for having nowhere to stow their hoods, which when lowered just piled up in clumsy fashion on top of the rear bodywork. There is none of that nonsense with the CLK cabriolet.

The three-layer hood is well insulated and fits solidly over the windscreen. It is raised and lowered by an electro-hydraulic system but, curiously enough, needs a heave from the driver to begin its rearward movement.

Watching the hood retract is quite an event, because as it moves backwards a metal cover behind the rear seats rises to accommodate it. Once it is stowed, the cover lowers itself again, and a perfectly smooth body line results. There is, of course, some reduction in the luggage space when compared with the coupe.

Like most models in the Mercedes catalogue, both styles of CLK seem to be well built and thoughtfully presented. Mercedes does nothing in the engineering line without a sound reason, and niche models like coupes and cabriolets are presented with the same attention to detail as the mainstream saloons and estates.