Launched at the Geneva Show in 1996, the Jaguar XK8 would do most of us just fine as a powerful and very stylish coupe or convertible. After all, it comes with the four-litre AJ-V8 engine which is not short of either brake horse power or torque.

A supercharged version then materialised in the XJR sports saloon, and it did not take a degree in rocket science to predict that it would soon percolate through to the coupe and convertible. As of today, here it is, in the majestic Jaguar XKR.

Bearing in mind that several extra-cost options on the XK8 are standard on the XKR, the prices of #59,300 for the coupe and #66,300 for the convertible look exceptional value against the supercar opposition. Tastes in whether to have an open or closed version will vary from country to country, but the expectation is that the split in UK sales will favour the coupe by about 70:30.

Computer controlled suspension, striking 18in cast alloy wheels, headlamp washers, powered fold-back door mirrors, cruise control and a CD autochanger, as well as wood and leather interior trim, are all standard features on the XKR.

But this is a car whose power output has been boosted to no less than 370bhp, with a skyscraper torque figure of 387lb ft at 3600rpm. The coupe will hurtle to 60mph in about 5.2 seconds, the heavier convertible being just a whisker slower, and both models have a governed test track maximum of 155mph. Serious technical modifications were needed.

Compared with the unblown XK8, the new car has uprated brakes, suspension, steering and tyre specification. A great deal of work has been done to keep noise levels low, and the bonnet louvres are not just an XKR styling cue. Together with the little boot lid spoiler they ''tune'' the airflow over the bodywork, and their third task is to help the airflow through the cooling system.

The XKR looks terrific at a standstill. You can see one or two items which have been procured at quite modest cost rather than being specially produced for the new car, but the exterior appearance of the coupe is gorgeous, and the convertible has an extremely well fitting hood which does not greatly affect the overall line.

So, how does the XKR go? It goes like a rocket, but even when you bury the throttle in the carpet there is a remarkable lack of drama. This is a supercar which simply gathers speed at a phenomenal rate, without any fuss or mechanical bother, and it is a supremely relaxed high speed cruiser.

But it will potter along happily at lower speeds too. As regular transport, untemperamental in traffic, the XKR has many of its ultra high performance European rivals licked to a frazzle. It fits in with the prevailing conditions, and does not keep you on tenterhooks all the time.

The keynotes of the car are refinement, flexibility and effortless torque. Even when it comes on song, the twin-intercooler Eaton supercharger is not obtrusive, but simply an attractive extra ''power'' sound. Of course, there is no turbo lag. Another appealing advantage over most of its rivals is that the XKR retains an unexpectedly good ride quality. Cabin details, control layout and so on are all as in the XK8. The J-gate gear selector is also the same, although the Mercedes-built automatic transmission has been tinkered around with a little to cope with the XKR's substantial extra power output and maximum torque. While the semi-manual side of the gate allows the driver not to depend on kick-down all the time, I wonder how many people will do anything other than leave the whole gear-changing business to the electronic gremlins.

The coupe just wins the concours d'elegance competition, and the fact that its price has been held just below #60,000 is a big plus point. On the other hand, the convertible is a fine adaptation, snug and good-looking with the hood up. But hood-down, there is a lot more wind buffeting in the cockpit than I enjoy.

In Jaguar's early days, company founder Sir William Lyons could style a car to look 20mph faster than it really was. The XKR is a different matter altogether. Its performance is right up there with the attention-grabbing appearance.

If you insist on having a supercar which is noisy, twitchy and difficult to see out of, needs a white-knuckled grip on the steering wheel and has to be kept on a tight rein all the time, forget the new Jaguar. It has nothing to offer you.