ECONOMY and sports roadsters have never exactly gone hand in hand down the highway of happiness but one marriage made in heaven is the diesel-powered SLK 250 CDI from Mercedes-Benz.

The SLK has always been a tremendous favourite of the petrol-powered lobby but the introduction of a four-cylinder diesel under this hallowed bonnet did not come as a surprise.

In fact it puts this 204bhp two-seater at the top of its class in numerous respects.

Boasting fuel consumption of 56.5mpg on the combined cycle, it is the most economical roadster in its class.

One of its secrets is enormous torque giving it acceleration worthy of a six-cylinder petrol because it can zoom from 0-62mph in 6.7 seconds.

This, applied to the clever gearing of a 7G-Tronic Plus seven speed automatic transmission gives that sporting edge on winding country roads and on long motorway stretches.

It is also a very silent diesel and you have to keep reminding yourself that it is not a petrol car, especially when refuelling.

In true SLK style, it combines its accelerative nature with the highest quality appointments. Full marks go to the electric fold-back roof which operates at the touch of a lever and disappears into the boot, still leaving room for a reasonable amount of luggage.

When the roof is up, the car I drove featured a panoramic roof, an optional extra. This can be specified with Magic Sky Control enabling the glass roof to be changed from dark to transparent at the touch of a button.

The power and torque of the engine is as much as a much larger petrol engine. This makes it the most powerful diesel model in its class, and gives the roadster the potential for extremely sporty performance with a top speed of 150mph on tap.

It brings an element of environmental compatibility to the sports car market without taking away any of the excitement.

It returns 56.5mpg and emits CO2 emissions of just 132g/km, giving the economy stats of a hatchback.

How all of this has been achieved is due to an extensive package of innovative technologies. These include fourth-generation common-rail injection with a pressure of 2,000 bar and precise injection timing, as well as two-stage turbocharging. Like all SLK models, the SLK 250 CDI also features a start/stop system as standard.

It is probably the first Mercedes two-seater capable of driving from the North Sea to a beach on the Mediterranean non-stop. Very comfortable sports seats, a comfortable suspension setup and the largest luggage capacity in this segment also do their bit to create the right conditions.

Costing £36,620 before options, the AMG Sport version I drove was steeped in AMG bling including special bodystyling and chrome tailpipes.

The car also featured a dynamic handling package as extra which enhanced its already predictable and sure handling qualities in no uncertain terms.