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HERE’S a factlet for you: modern diesel engines are currently at their peak of efficiency.

For high mileage users, they are the only practical choice – offering durability, refinement, performance and big-range economy.

With the use of AdBlue, exhaust gas recirculation and particulate filters, they are not as polluting as their tarnished reputation suggests, either.

But the development of a new car takes a long time. From the moment the product planners decide to press the go button, it can take between three and five years for it to arrive on a customer’s drive.

So there’s a great deal of crystal-ball gazing involved and sometimes that massive leap of future guessing goes awry.

This year, the diesel/petrol ratio has flipped completely with petrol engined versions outselling diesels for the first time in decades.

This phenomenon applies mainly to smaller cars but diesel demonisation is definitely consumers.

The situation is probably driven more by worries about future values than air quality concerns.

Maybe three or five years ago, the new Audi Q8 with its enormously powerful diesel engine would have seemed a very good idea on paper.

The Q8 is not a subtle car. Part swoopy-roofed coupe, part macho

SUV it ploughs the same look-atme furrow as cars such as the BMW

X6 or maybe the

Range Rover Sport – cars loved and bought by fans of conspicuous consumption the world over.

Using Audi’s fabled Quattro all-wheel-drive platform this five metre long, two-tonne behemoth is powered, at launch, by a three-litre sixcylinder diesel engine (and a mild 48v, taking hold among

10ah hybrid system) until a petrol variant arrives early next year.

In the top “Vorsprung” trim level there is also four-wheel steering to quicken the big car’s responses. Somebody asked me on social media what it was like to drive. “Like an Audi,” I replied, kindly. But with a couple of caveats.

Like any new car appearing out of any VAG brand, the new

Q8 is dripping in technology.

It’s got HD Matrix LED lights, lanedeparture, voice control and fourzone climate control. There are also five radar sensors, five cameras, 12 ultrasound sensors and a laser scanner to control a myriad of collision mitigation functions. This is all fine, obviously…until it doesn’t work. Twice on my test route, the car thought stationary objects were pedestrians and slammed the brakes on hard. One of the objects was a wheelie bin at the end of someone’s drive. The other was a council salt store. Thankfully, nobody was close behind.

The other un-Audi feature was the lag between asking for drive and getting it.

Two things are at play here – one is the time it takes the turbo to spool up some boost, the other is the time it takes for the eightspeed gearbox to react.

This behaviour is just what you don’t want when you’re turning right across an oncoming lane with fast approaching traffic. (heart-rate through the Alcantara-lined roof.)

For such a massive car it’s stupidly fast when it does get going.

It has the sort of in-gear acceleration that would comfortably flatten your golden retriever to the inside of the tailgate. After a short delay, obviously. Like in the big VW SUVs, the Audi’s lane departure steering reaction is really intrusive, fighting the wheel against you as though a tyre suddenly deflated. You can turn it off, of course, (or indicate every time you want to cross a white line) but the side effect of all this electrically powered, semi-autonomous potential is a noticeable lack of steering feel and feedback.

People will buy the Q8 because of what it looks like and what it represents. They will probably love it, too.

Me? I can’t see the point of the Q8 when there are so many good cars – ones that are fun to drive – in the Audi range.

And I can’t help thinking that if Audi knew back then what it knows now, this car might not even exist.