With list prices starting at more than £55,000, Audi A8 running costs could never be considered affordable, but even those with the disposable to actually buy one occasionally like to watch where it goes. And if that’s the case then the 3.0-litre TDI is where the smart money is.

Driven gently this large executive saloon is theoretically capable of 47.9mpg (pre 2013 models can hit 44.1mpg), though in reality you’ll be doing well to see anything above 42mpg in regular use. The good news is that even at that rate, the 82-litre fuel tank won’t be empty for at least 750 miles.

Those that are worried about fuel costs in particular should steer clear of the W12. Although it now employs active cylinder deactivation, where six of the twelve cylinders stop working under light throttle loads, the best figure achievable is 24mpg, with a realistic figure likely to be just the wrong side of 20mpg.

Don’t expect maintaining an A8 to be cheap, but take comfort in the fact that Audi dealers are normally excellent at looking after customers.

Large luxury saloons are rarely environmentally-friendly but Audi A8 emissions have always been competitive, and the 2013 revisions have improved on this even further.

The early 3.0-litre TDI managed 169g/km, but the latest model (with an extra 8bhp) manages to drag this figure down to a very reasonable 155g/km. That’s not far behind the 147g/km Hybrid, and we’d wager it’ll be more efficient and economical in the real world.

Even the 381bhp 4.2-litre TDI emits less than 200g/km.

By far the worst is the W12 model, which is rated at 270g/km – though with just under 500bhp you can soon forgive it any dirty habits.

Like its German counterparts, BMW and Mercedes-Benz, Audi A8 reliability is a key strength and a reason why most owners stick with the brand. That’s not to say it’s flawless though and minor problems aren’t unheard of, but they are thankfully rare.

So far there’s been no official recalls for the current generation of Audi A8, and any faults that do crop up are usually taken care of quickly and effectively by the dealer.