Key facts:
Model tested: Mercedes CLS 350 CDI
Price: TBC
Date tested: October 2010
Road tester: Richard Dredge

When the original Mercedes CLS debuted in 2003, it was genuinely different. A premium four-door coupé, the CLS was an E-Class underneath, but with 170,000 examples finding owners, it proved that style counts in the executive sector. An all-new CLS arrives in the UK in March 2011; has it got the substance to back up the style?

Sleek, stylish and beautifully built, the new CLS doesn't quite have the impact of its predecessor. The more upright grille gives the car a less sleek look than before, while the slightly overfussy exterior styling makes the car more aggressive but less subtle.

However, the new CLS is more efficient, as it's significantly more aerodynamic. With drag cut by around 10 per cent, fuel economy is improved and so is refinement; things are helped by more efficient engines too.

Of the four powerplants available, all are more economical than in the outgoing CLS. The two petrol units (3.5-litre CLS 350 and 4.7-litre CLS 500) feature stop and start technology, with a seven-speed automatic gearbox standard on all CLS models.

However, more than 90 per cent of buyers will probably choose diesel power. At launch there will be just the 3-litre V6 350 CDI, but soon after the 1 March delivery of the first cars, a 250 CDI unit will be introduced.

Carried over from the previous CLS, the 350 CDi engine has 265bhp and 457lb ft of pulling power, yet it can achieve 47mpg while emitting just 159g/km of CO2, making it 21 per cent more efficient than the previous model.

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Muscular, refined, durable and economical, it's a pearl of an engine that suits the CLS perfectly, as it hustles the car along at high speed in near silence, while sipping fuel rather than gulping it.

Once the 204bhp 250CDI engine is offered however, it's likely to prove even more appealing. The 2143cc unit emits just 134g/km and averages 55.3mpg, but it's still capable of 151mph and 0-62mph in just 7.5 seconds.

Whichever engine is fitted, the cabin is a great place to be. With a wide console that runs the length of the interior, the CLS is strictly a four-seater only. Leather trim is standard while the ride is cossetting and the seats are fabulously supportive, front and rear.

Rear seat space is still quite tight for anyone well over six feet tall though, but there's a large boot; long but fairly shallow, it can accommodate 520 litres.

Once ensconced in the cabin, it's truly luxurious with premium materials everywhere and plenty of standard equipment, including safety kit galore. Nine airbags will be standard and there are plenty of high-tech features such as LED headlights.

With the arrival of the new CLS still months away, prices and specifications aren't yet confirmed. Don't expect much of a change from the current line-up though, which starts at £48,400 and runs to £77,960 for the outrageously fast CLS 63 AMG.