Road Test: Audi A6 2.0 TDI Ultra S Line 4dr S Tronic

This is the mildly facelifted Audi A6 with a highly economical four-cylinder diesel engine and front-wheel drive. One to file under the ‘dull but worthy' file, you will no doubt agree.

You'll have to pay attention then, to spot the mild upgrades: the headlights (xenons as standard for the UK), air inlets, bumpers, side sills, rear lights and exhaust, as well as the ‘singleframe' grille, have all been subtly tweaked. There are new trim options too, changes to the MMI interface and acoustic glazing for the windscreen and front windows. As ever, the interior layout and quality remains without equal.

It's the drivetrain, though, that's of primary concern here. Audi has ditched the CVT slushbox in all FWD A6s and replaced it with the 7spd dual-clutch S tronic gearbox; the main cause behind the extra fuel economy and lower CO2, thanks in part to a coasting function.

The stop/start system has also been tweaked, which means if you opt for the entry-level 2.0-litre TDI ultra, you get an extra 3.1mpg (now 67.3mpg) with CO2 emissions dropped by 5g/km to 109g/km. Yep, that's the kind of margin here.

That 2.0-litre diesel is an affable unit, too. As with most four-cylinder diesel engines, it's grumbly when you've got your foot pinned to the floor, but offers performance of a punchy nature, and settles into a nice, quiet, relaxed canter once up to speed.

Combined with the A6's standard handling nuances - inert, accurate steering, comfortable suspension if you configure it right - it's an incredibly easy car to live with. Should you be so inclined, you could do big miles in a car like this.

Naturally, we'd advise you to opt for the bigger, 3.0-litre V6 engines on offer if you're adamant about buying diesel, because they're more powerful and quicker. The 268bhp version of this engine is the one with the most change: up 25bhp and down 16g/km of CO2, it's a stonkingly fast car. Go harder still, and you'll want the 318bhp BiTDI. It's a superb engine with Herculean reserves of power and torque.

There's much to recommend, and it's a beautifully appointed car. Yet it still lacks the driver sparkle offered by the BMW 5-Series.