I trust Audi won't take too much exception at a mention of the opposition but the first properly quick car I ever drove was a 1991 BMW M5. I recall the occasion clearly. It was a friend's car and he needed his brake pads replaced. Claiming to be able to do this job for him, I collected the car from his house and proceeded to spend all day driving it faster than a car with barely functioning brakes properly ought to go. 315bhp seemed such a ludicrously obscene amount of power from a four door saloon. Fast forward to the present day and Audi can trump that. With a diesel.

Yes, you did read that last bit correctly. The latest Audi A8 4.2 V8 TDI quattro is good for a whopping 323bhp. What's more, the BMW's torque figure of 265lb/ft is comprehensively knocked into the stands by the Audi's 480lb/ft figure. There may be some of you who feel that selecting a sports saloon from the start of the last decade represents a rather soft target, so let's shift the Audi's targeting system onto something bang up to date. Mercedes have nothing remotely comparable, nor do Lexus and Jaguar. Even BMW's range-topping 7 Series diesel is over 100bhp off the pace, such is the superiority of what Audi bill the world's most powerful production diesel. Only the 313bhp V10 TDI fitted to the A8's cousin, Volkswagen's Phaeton, gets in any way close but let's face it, you'd need to have a disregard of residual values bordering on the criminally negligent to opt for the Volkswagen over the Audi.

There are those that don't really understand diesel luxury saloons, reasoning that if you have over £60,000 to spend on a car, it's unlikely that fuel economy is anywhere near the top of your priority set. In a way they'd be right too. Fuel economy isn't the driver for buying an A8 4.2 V8 TDI, but if you're interested, it's pegged at a combined figure of 30mpg - 0.6mpg up on its 4.0-litre TDI predecessor. These cars are instead all about pulling power and the effortless surge of acceleration that accompanies that huge swell of torque is something only the very finest petrol engines can come close to replicating. This car isn't just fast for a diesel. It's fast, period. Flog it off the line and it'll trip the stopwatch to 60mph in just 5.6 seconds, which is half a second faster than the classic BMW M5. Like the BMW, it'll keep going to 155mph, but unlike the 5 Series, it'll manage up to 590 miles on a full tank of fuel. Black pump, remember.

"This car isn't just fast for a diesel. It's fast, period"

A full 15kg lighter than the 4.0-litre eight-cylinder TDI it replaces, the compact 4.2-litre unit is the first Audi V8 TDI engine to incorporate the latest common rail fuel injection system with state-of-the-art Piezo injectors. The precisely metered fuel delivery that Piezo technology makes possible ensures that the new twin-turbocharged and twin-intercooled engine not only provides more power and even stronger performance than the 4.0 TDI, but also holds that marginal fuel economy advantage. Featuring a separate high-pressure pump and rail for each row of four cylinders, the Piezo system permits up to five separate amounts of fuel to be injected on each working stroke at an injection pressure of 1600 bar, 250 bar more than with previous common rail systems. This helps to achieve the best possible fuel/air mixture and an even more efficient combustion process. Environmental impact is also minimised by a diesel particulate filter, which is fitted as standard and works in conjunction with the twin catalytic converters to maximise exhaust gas cleansing. The system needs no additives, and so will need no servicing throughout the lifespan of the car.

The 4.2 TDI takes its place at the head of a recently improved A8 range. The current model benefits from a smarter design for the trademark single frame grille, LED indicator strips in the side mirrors and LED tail lights. The 4.2 TDI variants cost from £61,595 and there's a choice of SE or Sport trim, plus short or long wheelbase bodyshapes. They include equipment such as 18-inch alloy wheels, full leather upholstery, a six-speed tiptronic transmission, adaptive air suspension, acoustic parking sensors, cruise control and the Multi Media Interface (MMI) control system. Heeding the flak BMW took when they introduced their iDrive interface into the 7 Series, Audi responded by offering a simpler, more intuitive control system. Like iDrive, MMI features a rotary knob that marshals a bunch of functions indicated on the dash-mounted LCD display. Unlike the BMW system, it doesn't throw too much information at you too quickly. Whereas it's possible to change the rear damper settings on a 7 Series when all you wanted to do was blip up a little more air con, the Audi system feels altogether less threatening.

It's but one feature in an interior that now looks like it belongs in this rarefied atmosphere. One criticism that could once be levelled at Audi's otherwise impeccable interior design was that buyers of the top line A8 weren't getting anything markedly different to the rep who'd lucked into an A3. The themes were all the same, many of the materials felt much alike and there were so many common parts. Great if you're the one with the A3, but not so good if you want something a little more exclusive. Audi has recognised this and has given the A8 an interior quite different to the usual classy coalhole. The instrument dials are raked back and trimmed with a light metallic theme that is dotted about the cabin.

Mechanical improvements to the latest A8 range include a re-engineering of the rack-and pinion speed-dependent steering to permit a more direct feel, and revision of the dampers, supports and general settings of the adaptive air suspension designed to give the A8 even tighter body control through corners and an even more unruffled ride. In conjunction with these measures, supplementary insulation using innovative new materials has also been added throughout the car, the result being that the A8 now records the lowest rolling, road and ambient noise levels in its class.

Like all A8 models, this one also benefits from specification enhancements. The 9-speaker, 230-watt sound system with six-CD changer is also now complemented by a DAB digital radio module for reception of ultra-clear digital broadcasts from an expanded choice of stations. Climate control is upgraded to a more sophisticated four-zone system with individual temperature and air distribution controls not only for front seat passengers but also for each of those in the rear. A8s also now benefit from heated front seats and Bluetooth mobile phone connection.

This is a technological showcase for Audi, a company that now feels confident enough to put its rivals ruthlessly in their place. As a candidate for best car in the world, it's tough to think of anything that can top the A8 4.2 TDI V8 quattro. It is a car with no Achilles heel.

TOP 3 A8 DEALS

The results below show the top A8 deals on buyacar

	Audi A8 4.2 TDI Quattro SE 4dr Tip Auto Saloon
	ETR	Mthly £1,017	Saving £8,169	Price £53,526
	Audi A8 4.2 TDI Quattro SE LWB 4dr Tip Auto Saloon
	ETR	Mthly £1,063	Saving £8,641	Price £56,424
	Audi A8 4.2 TDI Quattro Sport 4dr Tip Auto Saloon
	ETR	Mthly £1,058	Saving £8,526	Price £55,719

typical 9.44% APR

PCP finance quote over 48 months,  10,000 miles pa,  deposit of £1000