When heads of state, CEOs of multinational corporations and senior politicians get shunted between their palaces, corporate headquarters and seats of government, they use cars like this Jaguar. It's the long-wheelbase model of the latest XJ saloon, a car that's controversially done away with the traditional twin double-lamp headlights that purists say have always set the big cat apart from the herd of ruminants.From inside the protective formation of their bodyguards, the principal oozes out through glass doors into the street and down the steps to the car. They pause for a shot from the paps next to the subtly sparkling Caviar paintwork (I kid you not) before sliding their elegantly betrousered bottoms onto the yielding pale Parchment leather seats and waiting for the Burgundy leather-upholstered door closed behind them.With a good five inches of knee clearance between them and the driver in front, they fold down the in-flight tray to support the FT then finger the buttons to raise the electric blind on the back window, draw back the screen on the rearmost of the two sunroofs, adjust the temperature and direction of the air blowers and tune the heated and cooled rear seats to suit the day, the mood or the sciatica.What with the multimedia pack including TV screens on the back of the front headrests, there's more than enough to do to keep our VIP busy or entertained between Westminster and Heathrow, but this version of the car is missing potentially important equipment for the rear-seat passengers. There should be a crash helmet holder and a five point seatbelt in there, because this is a Supersport model and if the chauffeur decides to grind the pedal into the Axminster, this car will bark like an attack dog and leap out with just as much fury.Under the power hump stretching down that long bonnet is a five-litre V8 Gen III supercharged engine. The car may weigh almost 1.9 tonnes but 503bhp is enough to catapult it up to 62mph in under five seconds and on up to a top speed of 155mph. Given its incredible propensity for gripping the road and staying level through the corners, that back seat could become a hostile environment very quickly. Anyone in there when the power and glory are unleashed is going to want to be well padded and pinned down.The exec in the back probably won't care what the man with the cap in front thinks of the car, but I know he'll be very happy indeed. It's not just me that says it. The private hire, limo and chauffeur trade magazine Professional Driver has named the stretched XJ four-door as its Car of the Year 2010, beating off hot competition from the prestige German marques for the first time.OK, the winning car had a diesel engine, but for sheer, uncompromising driving, the Supersport is the one. Only 5% of all XJs in the UK are expected to have the fire-breathing engine under the hood but you won't need to read the monograms on the vents to spot them – the drivers will have very wide grins indeed. Oh, and when their passengers have been deposited at Departures, they'll be taking the scenic route back to the garage, via Dartmoor, the Lakes or the high moors of Caithness and Sutherland . . . whichever is furthest.Setting aside the seemingly interminable list of standard kit and optional extras, the driving experience can be as involving and exciting as you care to make it. Leave the beast in its default settings for suspension, steering resistance, engine response and automatic gearshift, you can tool home along the motorway on cruise control virtually without touching hand or foot to anything other than the steering wheel. Select your settings more, let's say, creatively, and the world becomes a much more interesting place.Jaguar no longer has the famed J-gate gear selector – now there's just a big knurled knob of bright chromed metal that rises out of the centre consol when you start the engine, and you turn it to the gearshift you want. Alongside the standard park, reverse, neutral and drive settings, you have S for Sport. That makes the engine rev a bit higher before changing up a gear. Stab the button below with a label that looks like a chequered flag and you've selected Dynamic mode. With Sport and Dynamic selected all gearshifts have to be made with paddles under the steering wheel – tug the right for an upshift, left for down.Snaking up into the mountains on the paddles in late summer sunshine is a joy. The gearchanges are very fast and very smooth, and unless you exercise almost superhuman restraint you'll find the bottomless well of power has provided you with all you need to lose your license if not your liberty for a very long time indeed.Taking a languid break from the succession of hard slick-snaking corners and the cheek cramping grins, it's a lovely thing to get out and walk around your ticking and cooling car. Unlike many long-wheelbase cars, the XJ doesn't look disproportionately long in comparison to its width or height. If anything that tapering chrome trim that encompasses the side windows looks all the better for being a bit longer than it is in the standard car.Faltering just a little at the thought of a Jaguar saloon car without the two-by-two light configuration, I have to admit the new narrow light look is a winner in the Mike Grundon book of aesthetics. The tail lights on the other hand look a bit unnecessarily drawn forward over the car's haunches, giving it more of a transatlantic feel than is strictly tasteful.Conversation-worthy features on the car must include the virtual dials on the dash. Basically instead of a conventional speedo and revcounter, you're looking at a small telly screen on which is the projection of the essential dials. A photograph of them doesn't do them justice as they look just like the genuine article.By contrast, the Bowers and Wilkins audio system is a conversation killer, pumping out as it can 1200 watts of the finest digital reproductions of everything from the LSO to ELO or REM depending on your taste in sounds. The system also accommodates almost any mode of contemporary recording you can think of, bar LP or quarter-inch tape.It's not an unusual feature these days but I find push-button opening and closing of the boot is always a cool thing. I understand if you can be bothered to read the instruction book, you can customise just how open the boot lid goes on the XJ.I'll say now there are a couple of features I feel are unnecessarily plebeian inside this car. Call me picky but I feel if I'm spending £91,000, the gearshift paddles could be made of something a bit more substantial than rather brittle and cheap-feeling plastic. I'd also like my chronograph clock mounted properly upright. The one in my test car was turned slightly off the vertical. A small thing, but surrounded by such opulence it was almost shocking.In conclusion, though, if you're looking for a sleek and elegant car that's convincing as a refined executive cruiser but with enough brutal strength to blow most sportscars into the weeds, you'll find it right here. Its strengths lie in much more than the kudos of the badge and it has delights for the occupants of the front and rear seats. Engine 5000 cc, 8 cylinders Power 510 bhp @6000 rpm Torque 461 ib/ft @2500 rpm Transmission 6 speed auto Fuel/CO2 23.4 mpg / 289 g/km Acceleration 0-62mph: 4.9sec Top speed 155 mph Price From £92481.00 approx Release date 01/01/2010