I remember we had a little Honda 50 motorbike when we were young that was so easy on fuel, we used to say it would go on the sniff of petrol fumes. And given the sparse resources we had at our disposal, it often did.
Its miraculous feats came to mind in the course of driving this week's test car, the luxury Audi Q7 e-tron diesel plug-in hybrid.
If you were to believe the official figures, this is capable of putting our little fuel-sniffing Honda to shame. They are extraordinary but, sadly, transpired to be fanciful in real-life driving. Audi claim this machine, with its 3-litre V6 diesel and powerful electric motor, conspire to reduce consumption to a mere 1.9l/100km (156.9mpg!) while whittling emissions to 48g/km (€170 road tax). Extraordinary? Yes, on paper; not on the road.
What was extraordinary was the performance, however. With a total output of 368bhp and a mega 700Nm of torque (major pulling power) it can sprint to 100kmh in 6.2 seconds. In other words, this giant is quicker than a Golf GTi.
Add in a hush-quiet, smooth drive, room for four/five (the battery pack robs you of the third row of seats unfortunately) and sumptuous comfort, and you have an exemplary piece of modern motoring. It is, they claim, the world's first luxury SUV plug-in hybrid V6 diesel.
The only trouble is that with my test car, which had the handling/ride enhancing air-suspension option, the price also takes off - to a whopping €103,000. So it is for the few who can afford, though it does serve to highlight what can be achieved.
But I do wish carmakers would treat us with more respect and not foist crazy MPG figures upon us. There is no way in the wide earthly world that this can manage anything remotely approaching the fantasy official figures.
Even if you arduously plug in to charge up the battery, drive evenly and avail of brake-energy regeneration - and everything else that the magician technology can conjure - you would, in my humble estimation, be doing really, really well to get 50mpg; more like 40/45mpg. That is still exceptional for a large SUV like this, but it's a third of what is claimed.
Yet, I also think all plug-ins - be it this, the BMW X5, Volvo's XC90 or smaller ones such as the Volkswagen Passat GTE - are beginning to serve a purpose for the longer term. They are helping us get our heads around regularly plugging in a car to avail of lower electric/running costs. And that is not so easy to do because we have been brought up to fill up, rather than tune in and plug in.
My cynical side says many people are buying these cars and pretending to be 'green'. They have no intention of charging up regularly, but unfairly avail of the incentives stemming from the official consumption figures which cut price and road tax.
My less cynical side believes there are some who see the likes of the Q7 as an opportunity to cut consumption/emissions. Equally, they can get their daily commute on electric charge only (I reckon it will do 25kms) and use the copious reserves of the diesel tank to permit much longer hybrid drives on business or at weekends.
Yes, you can argue the better-off are benefiting from our collective positive discrimination in terms of financial incentives and road tax. Be that as it may, there are many more of its ilk to come because those crazy, but credited, fuel consumption figures reduce carmakers' corporate emissions figures and help keep them the right side of ever-tightening regulatory limits.
But that's all big stuff. At an individual level, my few Honda 50 flashbacks aside, I paid little attention to such considerations when I was at the wheel of the Q7 e-tron. It was an outstanding, engaging drive. I'm sure the battery pack at the back aids overall balance, and I'm certain the air suspension played its part, but this was exceptional over motorway and bog road. I grew fond of it as I traversed the miles in its luxury cabin.
And I'm prepared to bet that if you had passengers, as I did, and told them there was a petrol engine under the bonnet, they would have wholeheartedly concurred, such was the 3-litre V6 diesel's quietness. It was only outstripped by its instant bursts of power.
And so the car was capable of silently (electric only) slipping out of the blocks, instantly accelerating when I slammed the foot down or just swishing along at motorway speeds.
As a diesel plug-in, this is out on its own; there isn't anything to touch it. Not even fond memories of the Honda 50 come close.
Facts & figures
Audi Q7 e-tron luxury 5-seater plug-in SUV; quattro, 3-litre V6 diesel (254bhp, 94kw electric motor); 8spd auto, 1.9l/100km (156.9mpg); 48g/km, €170 road tax. Price: €103,637.
Standard spec includes cruise control, 20ins alloys, 3-zone air con, Xenon Plus headlights, virtual cockpit, Audi Connect, leather upholstery, park assist. Options include air suspension (€2,824), Audi pre-sense (€345), charging dock (€386), alcantara upholstery (€2,130), Matrix headlights (€3,554).