A week is not nearly enough in Audi’s range-topper. It’s the normal loan period for an AM test car, but the A8L 6.0 W12 is no ordinary car. It’s an extraordinary car.

Within seven days, a prospective buyer may have figured out the limo class cruiser’s front and rear seat memory variables. But full familiarisation with the MMI (multi-media interface) terminal alone takes patience, diligence and, possibly, an experienced, professional chauffeur with more time than Autoglym cleaning fluid on his hands.

In a wad of eye-crossing information, Audi describes MMI as an “infotainment platform and operating concept noted for its ease of operation… that involved a constant dialogue between design, ergonomics and technical departments”.

It’s what BMW calls iDrive. But, like the BMW dealers into whom the fear of the Bangle Almighty was struck at the mention of the i-word back in the new 7-series launch days, Audi retailers are now pretty well versed in the explanation and demonstration of in-car infotainment.

We had it more or less sussed by redelivery time: the console knob, four control keys and eight function keys allow the driver to finger-tip the air suspension settings, ride height, radio, satnav, TV, CD, climate, phone et al. Options, menus and results appear on a seven-inch colour monitor, and there are rollers and buttons on the steering wheel which refine some of the functions.

The electronic architecture of communication, comfort and convenience (no, we didn’t find one of those) in the A8L is extensive. Shortly before returning the A8 to its maker, we discovered that rear compartment passengers can not only play with electronically operated back and side blinds as well as set the preferred ambient temperature, but give the front passenger the willies by altering the pitch, height and reach of the front passenger seat – without warning. A highly amusing and, no doubt, very useful distraction.

However, once the scores of possibilities are explored, mastered and set, most can be left unmolested (rather like the tip auto) for the main attraction of actually driving the 1,995kg aluminium space-framed A8L.

This is a big car – as can be vouched for by the glitterati who have been shipped to and from big occasions like the BAFTAs fleets of A8s – but it handles and rides with the agility, precision and confidence of a medium prestige sports saloon. At 5.192m the A8L is just 0.107m longer than a standard 8, but, as every actress knows, the extra few inches inside make all the difference.

The long wheelbase version has the choice of 3.0 multitronic and 4.2 quattro petrol, 4.0 TDI diesel and the 6.0-litre quattro. The first three are more than up to the job, but our test car had the VW Group 12-cylinder W-shaped 6.0-litre petrol engine. It’s a wonder in its own right; 0-62mph in a whispered 5.2sec and with the potential to whisk up to the limited top speed of 155mph in less than half a minute. It will stop quickly, too, without upsetting the driving line or the passengers.

Since the new corporate nosed A8 was introduced in June last year, Audi has sold a little more than 1,200 in the UK – pretty much the expectation in the luxury (read German) saloon sector.

The 6.0-litre engine accounts for about 80 of those sales to date, a rarity factor which one might expect to be reflected in the three years/30,000 miles residual value prediction from CAP.

It isn’t – CAP reckons 67% of the list price will have been wiped away in that time, leaving a residue of 33%. It just doesn’t have the well-heeled cachet of a BMW 760L (37%) but, interestingly, it is a short RV nose ahead of the Mercedes 600L (31%).

We’ve said it before, but we’ll say it again. If you can get hold of a three-year-old W12 for £25,000 in 2007 it will be the used car bargain of the year. And a beautiful, driveable limo to boot.

Strength: Supreme quality throughout
Weakness: Too discreet for the showy fraternity?
Opportunity: The corporate chauffeur market
Threat: In Britain, the Germans
USP: That W12
Price: £75,775
Engine: 6.0-litre W12, 450bhp/427lb-ft
Performance: 0-62mph 5.2sec, limited top speed 155mph
Transmission: 6spd paddle tip-auto
Efficiency: 20.2mpg (comb), 336g/km CO2
CAP RV (3/30): £25,400 (33%)
Service intervals: 9,000-19,000 miles
Rivals: Mercedes-Benz 600 Limousine Bi-Turbo (£94,250), BMW 760Li (£80,500)