Buying an Audi A8 is no way to tell the world that you can easily spend several tens of thousands of pounds on a single car. The A8 has a certain elegance, but it is so near the heart of Audi's design philosophy that an only half-attentive onlooker might wonder why they seemed to be standing closer to an A4 than they thought they were.There is nothing brash about it. Its joys are of a subtler kind. Perhaps the best example in this particular car is its three-litre diesel engine. It's not so much that it is adequately powerful, though that is certainly true. More important is the fact that it goes about its business with what must be approaching the feasible minimum of fuss.In gentle motoring it hardly seems to be there at all. Round town, you might almost be driving a hybrid. (You're not.) If, out of necessity or merely for the fun, you stamp on the accelerator pedal and hold it there until you hit maximum revs and the eight-speed automatic gearbox decides it's time to shift up, you can hear that there's an engine somewhere, but it might be in a different car, or you might be listening to a recording. Even in the most brutal of circumstances you don't have to strain to hear the radio, or raise your voice in conversation.On the EU fuel economy test, this A8 can average 47.1mpg. I fell short of that by only a handful of percent, and I have no doubt that I could easily have exceeded 50mpg if I'd tried. For a large luxury car, this is quite something.Audi has a habit of using the same interior design for wildly different models, which is fine if you're driving one of the more basic ones, less fine if you're in something more expensive. The A8 has some familiar features, but it feels distinctively different from most other Audis, as it jolly well should for the money.The positioning of the footrest might be improved. Audi recently went through a period of mounting these so far away that you had to stretch out to reach them, a strategy which completely ignored the whole purpose of having a footrest at all.The one in the A8 isn't that bad, but it's far enough away that it must surely have been designed for those who, like the clockwise haggis, have left legs longer than their right. And I realise that these people are God's creatures too, and their needs must be catered for, but I'm surprised that Audi thinks they represent the majority of potential buyers.It doesn't feel like it, but at £58,800 the SE diesel is actually the cheapest A8 there is. In its normal state it has 18" wheels, but the test car had 19s as a £1635 option. I'd stick with the smaller wheels, but if the larger ones were forced on me I would set the standard adaptive suspension to Dynamic and leave it there. In Comfort there's too much of a mismatch between the lower-profile tyres and the damping.The 19s were very far from being the only extras fitted to the test car. In fact there were so many that they bumped the price up to £73,505. Some were tempting but extravagantly priced - I offer the £1340 head-up display, the £1635 front-seat ventilation and massage and the £1530 alcantara package as examples of this.Adaptive cruise control is available for £1330, there's a Bose surround-sound audio (very good, no question) for £1175, and if you can spare another £460 you can have powered door closure, with which you can languidly send a door swinging towards the car but let the final sealing take care of itself. In terms of increased luxury feel per pound spent, this is by far the best option available. Engine 2967cc, 6 cylinders Power 254bhp Transmission 8-speed automatic Fuel/CO2 47.1mpg / 158g/km Acceleration 0-62mph: 6.1 seconds Top speed 155mph Price £58,800 Details correct at publication date