IT has been a long time coming but the Mercedes- Benz SLK-Class with a diesel engine has been worth the waiting.

The German car maker has added one of its 2.2-litre diesels to the iconic small two seater, which built a reputation and demand on a range of seriously sophisticated petrol engines.

Here you have the best of both worlds, a head-turning sportster and a very economical one at that.

Forget what you may expect of a diesel - slow, noisy, unrefined and smelly - but look forward to what you also associate with such uber-smooth engines, very good economy.

In today's market that is highly desirable and the SLK builds on that pleasure with its surprising sophistication which includes rapid acceleration, refined motorway cruising and rewarding agility.

Clever engine design, finely tuned electronics, and its  stop&start system give the SLKhead-turning performance without the driver raising a sweat.

There are a dozen models in the range now, from just under £30,000 to almost £55,000 using four power outputs in its engine range with six speed manual or seven speed automatic transmission.

The new diessel sits towards the middle of the range and comes with the sportier AMG package to sharpen steering, brakes and suspension.

Even so, it's a remarkably smooth ride without any noticeable twitchiness but a lot of inherent grip to match the grunt underfoot when you put pedal to metal.

With a carefully laid out cabin to put everything at the driver's fingertips and good instruments ahead you always feel in control.

Secondary switches are quite large and sensibly located as well and the heating and ventilation works very effectively. This particular car had a clever dimmable sunroof and I would recommend for the variable UK weather.

The two seats are on the thin side but surprisingly comfortable with adequate adjustment range so long as you do not mind sitting quite low in the car.

There's good oddments room in the cabin and the boot holds 225 to 335 litres depending on the roof position.

With the roof in place the rear visibility is restricted but there are big mirrors and effective wipers. Drop the roof and you have a clear view in all directions as it stows out of site below the boot-lid.

The 250 SLK is slightly deceptive. It's not a 2.5-litre engine but with dual turbo-chargers pushing you along you'd be forgiven for thinking it was larger than 2.2-litres.

Power comes in quickly from rest, there is a wide spread of torque, and as you move through the box, which you can fine tune to taste as well, the pickup is extremely smooth and unhesitating.

On the road it delivers an inspiring drive and now with the benefit of extremely good fuel economy, this is a roadster which fits the bill under any circumstances.