IN days of old, when the idea of Jeremy Corbyn becoming leader of the opposition in Parliament was still the stuff of deranged fantasy, anyone who fancied a saloon car with upmarket pretensions faced a pretty simple choice.
The BMW 3 Series, with its balletic rear-wheel-drive chassis and smooth six-cylinder engines, was where sporty types would put their money. Or, as is often the case with cars of this sort, their company's.
Anyone who could care less about the finer qualities of the BMW's driving dynamics bought a Mercedes-Benz 190E or C-Class, in the smug belief that their new car would probably outlive the Giant's Causeway.
Everyone else bought an Audi. First with its 80 and 90 models, and latterly the A4, Audi has traditionally offered a compromise of sorts: hints of the BMW's sportiness and style blended with the Mercedes's perceived prestige and quality.
Today, we have reached a point where not only is Comrade Corbyn the leader of the Labour Party but automotive evolution has hewn the three German makers' mid-size saloons into epically excellent cars.
In the 1980s, offerings from BMW, Audi and Mercedes sold in significantly smaller volumes than similarly-sized cars like the Ford Sierra, Vauxhall Cavalier and Austin Montego (remember them?).
Today, things have flipped round to the extent that the so-called premium brands are now mainstream; you are far more likely to see an A4 or 3 Series on the roads today than a Ford Mondeo or Peugeot 508.
Unsurprisingly, because of the sales volumes and the money to be made in this sector, Ford, Vauxhall et al have tried to follow their former customers' 'push to premium', albeit with little effect.
Volvo has a more legitimate claim to being a premium marque but still sells in small numbers compared to the German giants.
Lexus, too, has made a decent effort at challenging the status quo. However, despite the quality of its design and build, the IS saloon is destined to remain a niche choice for as long as it is hamstrung by its hybrid drivetrain and CVT gearbox.
The most significant disrupter to Audi, Mercedes and BMW thus far is Jaguar's recently-launched XE saloon.
It has already impressed greatly, particularly with the fluency of its chassis and steering.
When it first arrived last year, it was probably good enough to top the class.
The Germans were never likely to tolerate that for long. BMW has duly delivered an overhauled 3 Series, which Drive has yet to test, and Mercedes has a C-Class facelift in the offing.
But the most significant riposte is the car featured on these pages today: Audi's all-new A4.
Not only is it a major step forward on the old car but, more importantly, it also leaps to the top of the class.
At first - and even second, perhaps - glance it looks much the same as the previous A4. Such is Audi's way when it comes to design: slow and steady change, as opposed to radical reinvention.
It's a policy that has worked well for them in the past. Park old and new beside each other and the differences do reveal themselves.
The new car's bodywork, in classic three-box proportions, has the crisp, origami-perfect creases that characterise Audi's latest models, for example.
Nor does anyone else do the details as well as Audi; everything from the shape of the headlamps, the rear indicators' Knight Rider-esque animated flash, the grille embellishments, door mirror forms... it's all spot-on.
All of this matters with cars like this, but the feel-good factor from gazing upon the exterior fades compared to the interior's wow factor.
Audi has long held the crown for making the finest interiors available on a mainstream car, and the A4 is no different.
You realise that this is a special interior the first time you use the wipers, and wonder at the damping of the stalk. It is typical of Audi's approach that a function so mundane is touched by an attention to detail that helps elevate the whole car.
And this is Audi's greatness, if that is not too grandiose a description. Everything, from the heater vents and door pulls to the automatic gearbox's selector and the engine start and stop button, simply feels expensive. Even something costing Bentley money doesn't feel decisively more upmarket.
The test car was also equipped with Audi's so-called virtual cockpit, which swaps the traditional speedometer and rev counter clocks and analogue instruments for a digital screen.
Being digital, it can be configured in all manner of different ways. Want a widescreen satnav map? No problem; the Audi obliges. It sounds gimmicky, but it does actually make the business of operating the car a little easier. It's also the future; eventually, every new car will have a dashboard like this, but Audi got here first.
The seats are excellent, the quality of the leather top-notch and the squidge - a scientific term - in the steering wheel rim is perfect.
All this alone would make this mainstream, workaday car a truly special place to sit; Audi has gone a step further by making sure the A4 has loads of space for passengers too; who needs a larger A6?
On start up, the engine barely disturbs the cabin, and on the move the A4 possesses superb refinement. Noise and vibration just don't exist.
In fact, the more time I spent with the A4 the more convinced I became that this is one of the very best new cars of any sort that money can buy today. It's just so comfortable, quiet, relaxing, so easy...
An inevitable conclusion of that is the fading of the Jaguar XE's lustre. Niggles that might have been regarded benignly need to be assessed more forensically in light of the A4's brilliance.
And so the Jaguar is cramped, particularly in the back seat, and more difficult to see from. The British car's diesel engine is also rattly and obtrusive, its automatic gearbox swapping ratios less smoothly, compared to the library-quiet and über-smooth Audi. Nor is its interior a patch on the A4...
You get the idea; but such is the pace of change that you can be top of the class one month and a distant second the next.
One area in which A4 cannot quite match the XE is in the quality of its chassis and steering.
The Audi, however, is a big improvement on previous versions of the A4, and is by no means boring; the logic that says the 3 Series and XE are the only choice for the driver who enjoys dissecting a B road is no longer as irresistible as it used to be.
Bolstering the Audi's claim to be all things to all people is a dizzying range of engines and gearboxes, quattro four-wheel-drive and front-wheel-drive options and a wide variety of trim levels.
An Avant estate is, of course, imminent - there will be no XE estate - as are swanky Allroad models and a rapid S4.
Many elements make the new A4 stand out - the fabulous interior, its roominess and inherent quality, the air of hushed refinement and comfort and a feel-good factor that reveals itself on every journey, long or short.
But Audi's greatness is in how it weaves all of these together. And that's why it is the best car of its sort that you can buy today.
:: At a glance
Audi A4 2.0 TDI S line 190PS S tronic
Price: £34,030. As tested £41,782. Options included black leather and Alcantara trim £450, technology pack £1,450, vision pack £1,150, 19-inch alloy wheel upgrade £1,200, storage pack £175, acoustic glass £200, variable front seat head restraints £125, smoking pack £50, assistance/pre-sense pack £1,400, winter tyre package £1,552
Engine and transmission: 2.0-litre four-cylinder diesel turbo, seven-speed dual-clutch gearbox, front-wheel-drive; 187bhp, 295lb/ft
Performance: Top speed 147mph, 0-62mph in 7.7 seconds
Fuel consumption: 67.3mpg (EU combined); 45.9mpg (real world)
CO2, road tax, benefit in kind: 113g/km - not liable in first year, then £30 annually - 20 per cent
Euro Ncap safety rating: Five stars (90/87/75/75)
