STRANGE as it may seem, one of the most useful things on our old Audi A4 was the dash-integrated coin tray which, at a touch, smoothed out of the dash to reveal your parking and toll change.

Sadly there's no such thing on the A6, and it caught me out recently at the Dartford Crossing when, for the first time in living memory, I had to queue with the trucks and pay with a note rather than slip through the autotolls unhindered.

It's these small details that make the difference in everyday motoring, and which can have quite an impact on journey times. I reckon it took me all of four minutes to get through the toll booth which, if you are averaging 60mph, equates to four miles on the road – four miles nearer my destination.

The same theory applies to the time spent filling up: it stands to reason that the better your fuel economy, the less time you'll spend on the forecourt and the shorter will be your journey times. A real case of tortoise meets hare.

So it's good to report that, gradually, the A6's fuel consumption is improving. Last time, I reported an average of a disappointing 33.8mpg – a far cry from the official combined figure of 39.8mpg. Now, however, with more than 3,000 miles recorded and with the engine nicely loosened up, I've seen a marked improvement, up to 35.6mpg and often significantly more on a run. It does your conscience good, especially when compared with equivalent petrol cars: the A6 2.4 SE auto returns 28.8mpg combined, for example, while a Saab 9-5 2.0t SE auto is good for just 26.6mpg.

The Multitronic transmission has become more responsive, too, though there's still an annoying hesitation from a standing start. The quicker, smoother downshifts mean there's now no need to select manual mode if a quick burst of speed is needed for overtaking.

I'm relishing the A6's serene cruising ability and smooth ride which makes light work of a long motorway haul. And although the boot doesn't put the Avant among the biggest load luggers on the road, it's proved big enough for all the family's paraphernalia on a weekend away.

I'm less confident about the champagne-coloured interior's ability to stay pristine, however. It looks classy and feels great, especially with the walnut wood veneer inserts on our car, but I wonder how it will resist scuffs and stains over the coming winter.

Other criticisms? Not many, though I'd like a bit more power – answered by the latest spec 2.5 TDI which now develops 163bhp – and engine refinement could be better. Compare the A6 at tickover with, say, a BMW 530d or Mercedes-Benz E270 CDI and there's no contest on engine noise, though thankfully little seems to get transferred to the cabin.

Tax payable (40%): £203 per month