Many of the familiar arguments for buying a diesel-powered executive saloon don’t apply to the S4 TDI. The car’s relatively low CO2 emissions do help deliver a lower showroom price for the car than its petrol-powered opponents might have, thanks to relatively low first-year VED ‘showroom tax’ banding. The way that emissions-related company car tax bands are currently set, however, means those choosing the car as a fleet option won’t be rewarded with any less benefit-in-kind liability than they would have if they’d gone for a petrol-powered rival.

You’ll also need to pay for the fuel in your car’s tank out of your own pocket, rather than as a business expense, to see the sense in picking diesel over petrol on fuel economy grounds – and you’d imagine that plenty of potential S4 owners won’t.

Simon Davis

Simon Davis

Road tester
Rivals for the diesel S4 are thin on the ground, but it performs competitively against the Mercedes-AMG C43 and BMW 330d xDrive M Sport.

However, those who do should be very pleasantly surprised by the fuel economy that the car’s capable of. A test average of only just under 30mpg for our car may seem underwhelming – but a touring test result of better than 50mpg, representative of the car being driven at a steady 70mph, is quite remarkable for a car of this size and performance level. At that economy, the S4 could put almost 700 miles between fills of its 58-litre tank.

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