PERHAPS Audi should adopt Tesco's advertising line, emblazoned across a store near you: Every little helps. Although, in this case, it doesn't help much.

Audi, which is producing new models like Tesco stocks new lines of biscuit, wants owners to use as little petrol as possible.

So, many models shut off their engines when the car is stationary, restarting as soon as you lift a foot off the brake (in automatics) or dip the clutch, with a manual gearchange.

That's supposed to save a drop of the precious stuff, as well as pleasing the Euro boffins who measure tailpipe pollution: lower figures are good for city pedestrians and can cut your car's road tax too.

Which brings us to the rather handsome big (very big) Audi saloon driven here. It's a contender for (relatively) understated executive transport for the boss in a hurry, along with rivals like a Mercedes-Benz S-Class or BMW 7 Series.

Home grown Jaguar makes a credible alternative in the boldly shaped XJ saloon, although sales are modest. In the States, where a car as big as the Audi (and rivals) is simply everyday-sized, the all electric Tesla S is running riot with sales and arrives here later this year.

It'll be interesting to see how the Tesla saloon, with Aston Martin looks and a 300 miles range on a single charge, will fare in the battle for the CEO's parking spot.

Audi's offering, refreshed with a mild facelift and unique LED headlights earlier this year, is the fastest version of the A8 saloon on offer. It uses pretty much the same eight-cylinder twin turbo engine you'll find under the bonnet of a Bentley costing £40,000 more and you will not find it lacking in power.

Indeed, with permanent four-wheel 'quattro' drive helping out, it might be the quickest way to reach illegal speeds on a wet road with three chums you can find anywhere. And if the hit in the back doesn't shut them up, the noise from its four chromed exhausts surely will.

Nicely potent at idle and butler-discreet at a steady cruise, the refined bellow that follows a purposeful prod of the throttle will have a driver accelerating between speed bumps, simply for the noise from the rear.

Which won't help the fuel consumption one jot. With more than 500 eager horses on call, the S8 is never going to be a stranger to the filling station forecourt and is credited with a modest 29mpg in the official test all cars must go through.

Don't believe it; my shortish drive showed 19.2mpg on the nicely crafted dashboard and bettering 20mpg would add purpose to every journey. An 82 litre (18 gallon) fuel tank gives a still decent range and will be of more interest to someone who can afford an S8 than the rate it drinks petrol.

Suspended on air springs rather than steel, the S8 rides a typical British main road with an un-Audi like softness, nicely in keeping with its executive express brief and only occasionally hinting at a trace of bounce. It shrugged off the ride compromise usually inflicted by big wheels; the test car's optional 21in alloys (£1,565) merely adding to the car's road presence.

So, the S8 is big, comfy, very fast, beautifully built and equipped with lots of goodies. Bring it on, Tesla.

£79,915

513 bhp, 3,993cc, 8-cyl petrol engine driving all 4 wheels wheels via 8-spd automatic gearbox

155 mph

4.1 secs

49

29.4

225 g/km

35%

3yrs/60,000 miles