There comes a moment in every car test when suddenly you know; a moment when all the thoughts flying around your head settle into something sufficiently structured to form an opinion. The new Jaguar XK’s moment came half way through a curve on the best road I have ever encountered. And in that instant I knew that Jaguar was back.

The road is in South Africa, a length of highway that stretches to the vanishing point on the horizon, where you can travel at an average speed most UK-based cars will rarely touch in their lifetimes. An XK, above all, has to be a superlative touring car and despite some niggling issues such as too much tyre roar and not enough boot space, the new car is Jaguar’s best tourer yet. At 100mph it’s loping like most do at 60mph, its 4.2 litre V8 a reassuring, throbbing presence. On that road and at those speeds its ride quality was spectacularly good, its gearshifts silken perfection. This was looking promising.

The cabin is quirky but comfortable, carrying over the classically understated British ambience found in its XJS predecessor, but critically also providing the legroom so woefully lacking in the existing XK. For the first time you can even opt out of the slabs of walnut on the dash, and you should: they just look silly in such a car in the 21st century, while the aluminium alternative is not just more attractive but more relevant, too.

Most importantly the XK is a car you can drive fast and with minimal effort until the tank runs dry. Which is exactly what I did on that road, whereupon some nice chap from Jaguar filled it up again.

On the return trip the tank took rather less time to drain for now I was driving it in a way no Jaguar has asked to be driven since the ill-fated XJ220 supercar of the early 1990s. And that’s when the moment came. The XK was streaking down the road, V8 snarling malevolently, gearshifts now short, sharp and executed by pressing the paddles behind the wheel. As it turned into the corner I was aware of something more than the prodigious grip and fine composure I had experienced on the way out. This Jag was attacking the corner and suddenly it felt not like a sporting car, of which Jaguar has produced a fair few in recent years, but a sports car, of which there have been none.

I know my job is that of impartial arbiter but I’ll not conceal the joy that rose in my heart. For a moment I felt something I had presumed long dead: it was the spirit of the E-type.

But we should not get too far ahead of ourselves, for this is also a flawed Jaguar; it does not necessarily mark the end of the bad times for the troubled Coventry marque, nor is it the radical step ahead of the competition that Jaguar so regularly made in its 1950s and 1960s heyday.

Most disappointingly, its steering is not quite right, as if it can’t quite decide whether to play it soft and slushy as the Americans — who will buy half of all XK production — would want it, or instinctive and urgent as its European audiences will command. It’s quick and direct, but numbs the information about road conditions before it reaches your fingers.

When such a fine job has been done creating a chassis that has no problem combining sports car grip and poise with luxury car comfort, this missing component is as frustrating as spending a week on the 1,000-piece jigsaw auntie gave you for Christmas only to discover it contains 999 pieces. In this small but significant regard, the car feels unfinished.

Perhaps we should not be too delayed by this. When I think of the XK’s core rivals, the Mercedes SL 500 and BMW 650i, these are hardly sporting heroes either, and while a Porsche 911 would have been a paragon rather than a mere pleasure on that road, the XK is probably at least as good a sports car as the Porsche is a tourer.

Indeed those who buy the XK will probably be more concerned with how it looks than goes and all I can say on that score is that you’ll never gain a real understanding of how cleverly styled it is until you see one moving. In a showroom it looks a little odd around the front, but on the road it appears as all you could hope for from a Jaguar coupé: bold, muscular, flowing and really rather beautiful. I even cruelly parked it next to an early E-type, expecting the comparison to render the XK instantly awkward and derivative, and was amazed to see how comfortably it sat next to Britain’s greatest automotive design.

Which is one reason I rather wish I hadn’t then driven the convertible XK. I never got on with the last drop-top XK and this one continues the trend. It’s not as attractive as the coupé, it has even less boot space than the old XK cabriolet, and despite near identical chassis settings to the coupé, all the old structural compromises inherent in any convertible mean it’s nowhere near as good to drive, either. It’s not a bad car by any stretch and, if pushed, I’d probably just choose it over the ugly BMW 6-series convertible, but the steel-roofed Mercedes SL 500 is preferable by far, even taking into account its near £10,000 price premium.

All this is just the start for this new generation of XK. The 4.2 litre version goes on sale in the spring and will be followed by a cheaper 3.5 litre model in the summer before the one we’re all waiting for, the 420bhp XKR, arrives by the end of the year. Next year should bring at least one diesel XK and the XKR-R (not necessarily its final name), the car with which Jaguar plans to combat the BMW M6 and Mercedes SL 55 AMG.

Jaguar’s engineers refuse even to confirm its existence while simultaneously grinning like Cheshire cats, so expect 500bhp and, if they’re brave enough to take the limiters off, a top speed of at least 200mph. It should be something to behold.

Combined, all these XKs won’t right half the wrongs that currently trouble Jaguar but, as one senior staffer said to me: “You cannot imagine how bad things have been or for how long our backs have been against the wall. Well, we’ve had enough of it — the fightback starts here.” It’s early days I know, but from what I saw on that road I had no trouble believing him. No trouble at all.

VITAL STATISTICS

Model Jaguar XK 4.2 V8 coupé
Engine type Eight cylinders, 4196cc
Power/torque 298bhp @ 6000rpm, 310lb ft @ 4100rpm
Transmission Six speed semi-automatic
Tyres 245/40 ZR19 (f), 275/35 ZR19 (r)
Fuel/CO2 25mpg combined, 269g/km
Performance 0-60mph: 5.9sec. Top speed: 155mph (electronically limited)
Price £58,995
Verdict Fast and beautiful – a proper Jaguar at last
Rating 4/5

THE OPPOSITION

Model Mercedes-Benz SL 500 £74,125
For: Folding metal roof makes it two cars in one, good looking
Against: Very expensive and has only two seats

Model BMW 650i £52,115
For: Smooth and powerful engine, good handling, spacious
Against: Doesn’t look right, horrid iDrive control system