WHEN Jaguar boss Mike O'Driscoll said his company was in the entertainment business it was more than mere marketing hype.

Fun is the key ingredient in the latest generation of surprisingly capable machines from the famous British brand, now in its 75 year.

Power, performance and elegance have never been so pronounced as on the current crop of Jaguar models.

With the new XJ and XF setting fresh standards in the quality saloon market, the epitome of the Jaguar heritage is the XK sports car.

Now powered by a five-litre V8 it's fantastically potent but in its supercharged XKR guise it is simply breathtaking.

This fire-breathing 510bhp supercar is an equal to anything Porsche, Mercedes or Aston Martin can produce and now it has become even more special.

The latest XKR comes with the option of a speed pack which changes the engine's electronic mapping to push the top speed to an incredible 174mph.

The new maximum remains electronically restricted just as the 155mph top end of the ‘standard' XK is.

Such is Jaguar's engineering expertise the full potential of this amazing beast remains untapped.

To cope with the extra performance the XKR has advanced aerodynamics to help high speed stability.

The car's computerised active differential is also uprated to give more weight to the steering in ‘max out' conditions.

The result - in my book - is the finest drive you can get in any supercar costing less than £100,000.

The speed pack adds £3,500 to the £75,500 price of the XKR and it is available only on coupe models.

To push the style factor even further the car comes with a rear diffuser, body coloured side sill and red brake callipers lurking inside the 20-inch alloys. The cars are also set off with chrome surrounds around the windows, side vents and grille.

And if that is not sufficient, Jaguar is catering for those who demand something different by changing the brightwork to black gloss.

With the right paint finish - red or white especially - it is a very effective combination and the full ‘black pack' treatment combines black alloys and body coloured spoilers.

Go for black paint and there's almost a sinister air to the car but the optional XKR decals along the door sills cheapen a car of such distinction. Put the two packs together and the XKR is nudging £80,000.

That price bracket is true supercar territory - and that's where this Jaguar belongs.

Not only is the XKR so comfortable to drive it fits like a glove, the interior is a smashing blend of traditional Jaguar craftsmanship and advanced technology.

A rotary gear selector and electronic parking brake free up space over the transmission tunnel while the instruments are now backlit in white instead of green.

The fun starts the moment you get in and the starter button yearns to be pushed, pulsing out a red light in heartbeat rhythm.

Fire up the engine and the growl from the quad exhaust system is just what any V8 aficionado craves.

It gets even better with sports mode selected which electrically enhances the sound by altering baffles in the exhaust to elicit a thunder rarely heard on the road these days.

With absolute agility and a beautiful balance and feel the uprated XKR is bordering on pure GT perfection.

Such are the dynamics that the grip is leach-like and the ride totally composed.

Despite ratcheting up the top speed, fuel economy remains at 23 to the gallon - the same as any other XKR - and emissions are pegged at 292g/km. The 0 to 60 acceleration time of 4.6 seconds is also unchanged.

It is not rock solid a la Porsche but instead has a fluid feel all of its own - a special trait of a very special Jaguar.

If there is a quirk it comes with the sat nav and systems touch screen. Its predominantly grey and blue graphics may not be to everyone's liking while the plastic surround is more championship than premier league.

Yet it's premier status which the XKR Speed deserves. It is utterly exclusive, styled to thrill and drives so well it will impress the sternest of critics.

What's more is that it is all home grown - a fantastic mobile billboard for Britain at its best.