When I was 18 years old, my bank manager wrote to say he was disappointed that I had a £3,000 overdraft. This made him look like an idiot, because opening an account for an 18-year-old boy and then being “disappointed” when he runs around town vomiting cash into various pubs and clubs is like going to see a film starring Steven Seagal and being “disappointed” that it’s terrible.

If an octogenarian billionaire comes home from work to find his pneumatic 22-year-old bride playing hide-the-sausage with the handyman, he cannot claim to be “disappointed”, because surely, if he had any brains at all, he’d have seen it coming. If you employ a man who knocks on your door asking if you’d like a new tarmac drive, you cannot be disappointed when he sets your precious roses in 3ft of solid concrete and then sends a nightclub bouncer round with a bill for £400m.

I once went on a holiday to Tuscany and was annoyed to find when I got there that the villa I’d booked had an American family living in it, and that I’d have to spend two weeks in the spare room of a house two miles away. And then I was very annoyed that the owner turned out to be the head of the local Communist party and that he’d decided I needed to be lectured from dawn till dusk on the failings of capitalism. In Italian.

“Voglio uccidere i cestini di Thatcher di Signor e la marca fuori dei suoi capelli pubici,” he would rage endlessly, as I trudged up the road to the house where I should have been staying to ask the Americans if I could make use of the pool I’d paid to use.

But was I disappointed? No I was not. Because thanks to my bank manager’s disappointment, I’d booked the holiday on the cheap through an east London PO box that I’d seen in a small ad. I therefore knew before I set off that it couldn’t possibly end well.

Disappointment is a word for people who don’t think ahead; people who get themselves into fool’s mate when playing chess, people who buy a Hyundai Accent. It’s why I’m loath to use it.

And yet, in the motoring arena, I have to use it all the time because there’s no industry in the world capable of building up so much hope and then failing to deliver. You look at a company’s background, its expertise, its finances and the ingredients that are available to it, and you assume it cannot possibly produce a bad car. And then it comes up with the BMW Z8.

How did that happen? It had the underpinnings of an M5 and a body so beautiful I had an ache in the pit of my stomach when I first saw it. But it drove like everything had been attached to everything else with spit and two crossed fingers. It was awful.

Then there was the Ferrari 360. This came after the glorious 355 so we were all expecting more of the same, only better. But what we got was a twitchy little bastard with the face of a gormless frog.

And now we have the new Audi S6 Avant, which is fitted with the V10 engine from a Lamborghini Gallardo. When I first heard that this was being planned, I was — I’m ashamed to admit — priapic with anticipation. Audi had recently demonstrated with the RS4 that after years in the suspension wilderness, it had finally got to grips with the twin peaks of ride and handling.

Ally this to the traditional Audi qualities of good, understated style, exemplary quality, tons of estate-car practicality and that Italian supercar engine and you can see why I’d become a human tripod.

The only thing I didn’t know is what sort of car the S6 would be. Would it be a hunkered-down, super-sharp road rocket with exhausts like oil pipelines, five-point harnesses and tyres that had a lower profile than paint? Or would it be a true Q-car, a real wolf in sheep’s clothing? Smooth, quiet and dignified on the outside but with tons of quiet power in reserve. I began to slobber like a dog as I toyed with what path I would have taken if I’d been in charge.

What we’ve been given, however, is neither of these things. What we’ve been given is an ocean-going turkey, a lemon the size of Steven Seagal’s ponytail, and possibly the biggest disappointment in all of automotive history.

First of all, there’s the engine. Yes it’s lovely — no question about that. You’ve got a high compression ratio of 12.5:1 for glorious reserves of torque, you’ve got direct fuel injection, continuously adjustable camshafts, and the 10 pistons have 5.2 litres of space to move around in. Yum yum.

It’s a peach on the road too, always subdued, although under hard acceleration as you near the 7000rpm redline there’s a whisper of bass. It’s so faint it could be drowned out by Bob Harris but it’s there all right, reminding you that beneath the body of this station wagon there beats a thoroughbred horse.

Fine. But it produces only 429bhp. That’s just a gnat’s more than you get from the V8 in an RS4, and it’s nearly a hundred less than you get in a Lamborghini Gallardo. Why? Audi owns Lamborghini so it’s not as if the Italians have “lost” a hundred horses as some kind of latter-day payback for losing the war. And it’s not like the Audi boffins were wary of what happened the last time a mass-production car was given a monster engine...

The Lancia Thema 8:32 was a four-door saloon fitted with the 3.2 litre engine of a Ferrari 328. That didn’t work because you can’t expect a front-wheel-drive car like the Thema to be able to handle the power of a Ferrari V8. And so it turned out to be. But the S6 has four-wheel drive and could easily handle the full force of the Lamborghini V10.

So what’s gone wrong? Well, the Audi engine factory is designed to produce engines with a 90-degree Vee, but the Lambo’s engine has an 88-degree Vee. Ergo, if they were going to make the engine in an Audi factory, it had to be changed. That means the S6 has only 429bhp and that, in turn, means that every time you put your foot down, you feel a) cheated and b) like the car you’ve bought was designed by accountants.

You also feel like you’re not really in control because it has quite the sharpest throttle response of any car I know. It will only set off at full pelt, which is a nuisance when you’re having to contend with a gearbox that works like it’s on cannabis, and steering which — I feel sure — is made from old driftwood.

And then we get to by far and away the worst thing: the ride. They call it “S line”, and it doesn’t take too long to work out what the S might stand for. Clue: four letters, begins with S, ends in hit. Which is odd because it really isn’t one.

It’s not firm in a controlled way. It’s firm like the matron in a Carry On film. It’s firm to the point where you start to laugh at its complete inability to ride with grace or panache over absolutely anything.

I would love to meet the team who designed it, because I do not believe that anyone who has ever driven “a car” before could possibly have fitted this and thought it might do. Their bosses should certainly dig out their CVs and do some deep background investigation, because they’re either imposters or they’re secretly working for BMW.

I can’t be bothered to go on, frankly, because it doesn’t matter how much I like the styling or the quality, or wonder why you might want to spend £400 on an electric boot lid that closes at the speed of glacial drift; everything is overshadowed and ruined by the suspension, and to a lesser extent by the steering and the throttle linkage — which is as fast as the boot lid is slow.

Perhaps they wired them up the wrong way round?

With a tiny, tiny set of tweaks and a lot of mass sackings in the suspension design department, the S6 could be turned into something quite breathtaking. The ingredients are all there. But what you are being offered for £56,600 is actually well beyond a “disappointment”: it is actually utterly, utterly useless.

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