The Mercedes S320 CDi has few flaws as a luxury saloon. Even one of those can’t be entirely be blamed on Stuttgart burghers, but rather the vagaries of the British company car tax system, which saddles any diesel not Euro4 emission-compliant with a three per cent tax penalty. But that’s now been redressed with a clean-up for the 3.2-litre six-cylinder turbodiesel, courtesy of a particulate filter. There are some drawbacks to going greener, though. Extra-urban economy figures drop slightly, though improvements to urban fuel sipping make the overall figure unchanged at 35.8mpg. More important, CO2 emissions actually rise from 204g/km to 209. The tax burden will be the main interest to buyers, though, and without that three per cent bundled on it’s good news if a chunk of your salary is spirited away each month. If you’re a 40 per cent tax payer – and let’s be honest if you’re an S-class driver you will be – the latest version will set you back £459 per month, compared to the £493 you might have been contributing to Mr Brown in the dirtier diesel. Elsewhere it’s business as usual and that means the S320 CDi is still the most satisfying luxury saloon. It feels several degrees less agile than a Jaguar XJ or BMW 7-series, but retaliates with a rolling comfort and ride quality than no rival can replicate. For fast, unfussed cruising it’s a premier-league companion because of an almost uncanny ability to iron out small, sharp road intrusions as well as larger humps and crests. All the while you just grip the large, well-weighted steering wheel, virtually unaware that the air sprung chassis is busy isolating you from the outside world. As for that revised diesel engine, don’t believe the hype that it’s quite as creamy as the S-class’s six-cylinder petrols. But once it’s shaken off the admittedly subdued low-rev and cold clattering it’s a remarkably able motor. Free-revving, punchy when pushed yet languid on light revs, it’s more than in keeping with luxo-barge motoring. It’s not all superlatives, however. Just about every other luxury saloon is now showing Mercedes the way upmarket cabins should be constructed and the way they should operate. But with Euro 4 friendliness it seems a good bet that the S320 CDi will end its life as it began – as the best luxury saloon. Chas Hallett

Our Verdict

The Mercedes S-Class is a fine luxury car and a technological masterstroke. It is calm but rewarding

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