It is late afternoon on a crowded Italian motorway. Up ahead, a long black Audi sharks through the traffic, scattering battered Fiat Unos and Puntos before it like startled minnows. My co-driver frowns and wrinkles a brow, fixing a steady stare upon the middle-distant Audi. “Is that a new A6?” he asks. “Or is it an A8?”

And therein lies a clue to one of the most significant facts about this all-new Audi A6, launched last week in the suburbs around Lake Como and Milan. This is Audi going for gold in the executive class so viciously contested by the BMW 5-series, Mercedes E-class and Jaguar S-type. A major plank in the A6’s campaign is size, with swelling dimensions that move it closer to the luxury cruiser segment occupied by the A8, as well as the BMW 7-series and Mercedes S-class.

Indeed, this is a much larger car than the one it replaces, with an extra 3¼in between the front and rear wheels, 1¾in more width and a big 4¾in increase in overall length. In fact this is now the widest and longest car in its class.

So what do you get with the increased size? Well, there’s more legroom in the back, more shoulder room all round and a much bigger boot. In fact the boot is even larger than that in the A8. All this extra space means that four fellows of my size would be very comfy schlepping across the Continent in an A6. And I’m a good deal taller and wider than average. On any such adventure, luggage space just wouldn’t be an issue.

Bigger though it is, the new A6 still looks very Audi, a gently evolved and more aggressive version of the car that came before. That new corporate face generates the most visual drama — Audi calls it a “trapezoidal single-frame radiator grille”. It’s a bit out of keeping with the otherwise restrained elegance of the A6’s form, which gets a nice visual lift with the deep, rising swage line that runs the length of the car just above the bottom of the doors.

So the A6 is a handsome and well-proportioned beast. It just isn’t terribly exciting to look at, though that is true of most in this class.

Grab hold of the chunky door handle, climb in, crump the door behind you and settle into one of the finest feelgood cabins on the market. The quality’s there — given Audi’s track record, I’d be horrified if it weren’t — but it is the detail that really makes this cabin special. Even little things like the interior door handles are beautifully crafted bits of aluminium, and the aluminium inserts (you can have wood if you like) in the doors and around the centre console are equally gorgeous.

The new A6 also gains a version of the multimedia interface (MMI) system pioneered on its A8 big brother as a standard-fit item. This controls the radio, ventilation, navigation and other systems through the use of a single unit. If that sounds vaguely techno-scary, don’t worry: it really is one of the most intuitive and easy-to-use systems I’ve encountered.

You get a reasonable if not overly generous amount of standard kit with the entry-level A6 — the £24,175 177bhp 2.4 litre SE front-wheel-drive petrol model, which includes climate control air-conditioning, electric windows, 16in alloy wheels (too small, go for the bigger 17 or 18in ones for the right look), the MMI system and a CD player.

The petrol engine line-up rises to a 256bhp 3.2 litre unit with either front-wheel drive or Audi’s famous quattro four-wheel drive, and then to the daddy of them all, the 4.2 litre 335bhp V8 quattro. Until Audi decides to launch an RS6 variant, that’s the most powerful A6 we get and it’s the most expensive, too, at £42,775. But you do get an engine that punches very hard with a characterful snarl.

The lone diesel in the range is the marvellously smooth and responsive 225bhp 3.0 TDI quattro SE tiptronic, at £31,680. It will be joined later this year by an entry-level 2 litre diesel that Audi UK reckons will become the most popular engine choice here.

Audi is making another bold claim for the new A6. Namely, that it is the “sportiest business saloon in its class”. So why did they launch it to the press on some of the slowest and busiest suburban roads in Italy, with a few squirts of motorway in between?

Whatever, we did our best to push the car whenever a corner or roundabout presented itself — apologies to the guy in the red Golf, by the way — and found that the new A6 is composed and well balanced but lacks the sort of lively feedback through the steering and chassis that comes as standard with the BMW 5-series. As a result, this is unlikely to be a car to worry BMW on that score, but it is a superbly refined cruiser.

So then, overambitious claims about “sportiness” aside, the A6 has the space, refinement and “specialness” about its cabin to take the fight straight to BMW, Mercedes and Jaguar. It might even give the A8 a fright.

VITAL STATISTICS

Model: Audi A6 3.0 TDI quattro SE tiptronic
Engine type: V6, 2967cc, turbodiesel
Power/Torque: 225bhp @ 4000rpm / 332 lb ft @ 1400-3250rpm
Transmission: Six-speed semi-automatic, four-wheel drive
Tyres: 225/55 R16
Fuel/CO2: 34.0mpg (combined) / 223g/km
Performance: 0-62mph: 7.3sec / top speed: 152mph
Price: £31,680
Verdict: A refined, spacious and desirable executive-class contender

THE OPPOSITION

Model: Mercedes-Benz E320 CDI (£34,315)
For: That snob-value badge, elegant looks, ride quality
Against: Expensive, reports of patchy service from dealers

Model: BMW 530d (£31,900)
For: A fantastic engine and an engaging drive
Against: Looks too challenging for some