COST: £46,160  FUEL: 44.1mpg  CO2: 169g/km

Supposedly the diesel revolution is coming to an end. But it’s a sign of the times that, until the much thirstier and significantly quicker S6 arrives later this year, this twin-turbo 3.0-litre V6 diesel is the fastest A6 money can buy.

The question is, where exactly does this fit in the A6 range? Audi hasn’t marketed it as a diesel S6, despite a Le Mans-winning heritage with its TDI engines, and it’s caught between petrol-loving North American and Asian markets and a European executive segment which has downsized en masse to four-cylinder diesels. With CO2 emissions above 160g/km, there’s every chance top-level user-choosers will “settle” for the 156g/km, 245bhp single-turbo 3.0 TDI.

But the £4,700 price increase over its lesser sibling adds up to more than just extra power. This is an entirely different car, and a unique model in the UK now its closest rival – the BMW M550d – isn’t bound for Britain. A  sumptuous, luxurious executive saloon which also offers 62mph in just over 5 seconds, 308bhp and a massive 479lb.ft, and yet gives no visual clues that the default four-cylinder 2.0 TDI isn’t lurking under the bonnet.

Not that you’d have any doubt as a driver. The huge torque figure translates into effortless, deceptively smooth turns of speed, regardless of speed or gearing. This is a point-and-squirt straight line missile, which cunningly disguises itself as a comfortable German saloon car.

It’s a genuine Jeckyll and Hyde arrangement. With the DSG gearbox in its regular automatic mode it’s a relaxed cruiser that’s no more aggressive than a 2.0 TDI. Plentiful torque means it’s easy to keep the revs low, so the only thing that’ll keep you away from 40mpg fuel efficiency is the strength of your willpower.

Slot the DSG gearbox into Sport and, in addition to sharpening the already razor-like throttle response, it’ll give you a muscular growl from the twin exhaust pipes while accelerating. Though not as pleasing as a V6 petrol, but it’s nearly as addictive.

Verdict:

Think of the A6 BiTDI as the closest thing to a diesel S6 money can buy, short of neither the pace nor soundtrack to satisfy on an emotional level. But at 169g/km it’s a small-volume fleet car, an accomplished opt-out model for executives wanting power and economy in one very comfortable package.