Adam Hay-Nicholls

A limousine with the heart of a prize-fighter: Adam Hay-Nicholls slips behind the wheel of Jaguar’s sportiest CEO-wagon, the XJR-L.

Jaguar’s range-topping XJ was designed to be a refined, classy, wafting limo but the ‘R’ model has got its hands on the nuclear codes. A V8 developing just shy of 550 horsepower ensures that it overtakes its staid stable-mates sideways with a jet-stream of tyre smoke.

Small changes to its elegant looks give it a much tougher aesthetic, like the chrome-tipped supercharger vents in the bonnet, a little spoiler on the back, surround skirts, a mesh grille and, on my silver-coloured ride, big chunky black alloys and a two-tone black and white leather interior.

The XJ was already a very handsome car, one that looks a zillion times better in the metal than it does in pictures. Jaguars had been conservative for far too long, buttoned down with little hint of the curves that defined the 1950s and 60s. They’d begun to look like Fords with extra chrome and mahogany. This is a triumph of modernism. A piece of mobile sculpture.

I’m driving the long-wheelbase version of the XJR, which the hyphenated ‘L’ on its rump denotes. While most ‘R’ owners will want to do the driving themselves, having an extra 125mm of rear legroom means that if you prefer to take a backseat you’ll be doing so in presidential comfort. The extra length doesn’t hamper the car’s stylish lines, if anything it enhances its presence.

Yes, at first glance its back end seems unfathomably elongated even in Short Wheel Base spec, but ones eyes are soon seduced by it. It has the discrete muscle and powerful elegance that designer Ian Callum perfected previously at Aston Martin. In that sense, one could almost look upon the XJR as a cut-price Rapide S with plenty more space in the rear.

There’s more room inside than a convention centre, and swathes of leather, carbon fibre and chrome. The vibrant craftsmanship is meticulous, the overall look a successful meeting of sportive and serene, traditional and 2014. There’s a generous menu of gadgets to play with, but it’s not quite on par with the four-wheeled Radio Shack that is the Mercedes-Benz S Class. The svelte roofline compromises rear headroom, so you might need to ditch the Philip Treacy millinery. Road and wind noise is near-nonexistent, and the engine quiet at cruise.

The real difference with the R over the standard XJ is what happens when you nail the throttle. First of all, the sound that seeps through the double-glazing is this low, deep rasp a bit like the Johnny Cash tuning up his vocal chords. The acceleration is thundersome. Zero to 100km/h in 4.4 seconds, and it feels faster. It’s so improbable for a car that stretches 5.1 metres. What’s even more impressive, and useful, is its sprint from 80 to 120. Under 2.5 seconds. That’s what 502 lb/ft of torque will do.  I suspect it can race to its electronically-limited 280km/h redline with its passengers pinned to the headrests all the way.

Its fully aluminium body keeps it under two tonnes, which is light for this class of car. Lighter, in fact, than the smaller XFR that sits below it in Jaguar’s line up.

With the road ahead clear I press a button with a chequered flag on it, engaging Dynamic mode. The digital dashboard goes from white to red, like its blood has started flowing after a chill. Clicking the gearbox selection wheel (which rises electronically from the transmission tunnel like the periscope on a submarine) to ‘S’, I now have quicker shifts, harder suspension and more responsive steering and throttle. Despite its girth, the XJR feels utterly composed round long, fast turns. It was developed on the world’s most notorious racetrack, the Nordschleife.

Presidents and plutocrats like their legroom, but they don’t like to hang around and here it’s the Jag’s ride as much as its power that’s vital. Rest assured, your chauffeur will be able to J-turn out of sticky situations without you spilling your espresso.

The springs are 30 percent stiffer and the tyres ultra low-profile, so while the ride is smooth by most standards it lacks a little bit of the magic carpet feel of other big Jags. When faced with a corner, though, the dramatic reduction in roll will help keep your power lunch down. Its active damping adjusts 100 times a second to keep vertical movement in check. It’s as composed as Magnus Carlsen on a chessboard takedown.

‘R’ is Jaguar’s performance sub-brand, like BMW’s ‘M’ department, and Mercedes’ AMG. There’s sadly no M7 (although there is the unofficial Alpina B7), but Merc’s much more expensive S63 AMG and Audi’s slightly more discreet S8 are the XJR’s closest rivals. The Germans excel in the details – an almost irritating degree of perfection. There’s nothing prissy about the Englishman, however. The Jag has the most emotional appeal. It has swagger. If you met a bunch of super-saloons at a party, you’d want to hang out with the XJR and the Maserati Quattroporte.

Jaguar’s heritage of ‘gangster chic’ – the promise of shooters in the boot and Cutler & Gross specs in the sun-visor case – lends the XJR an earthy, thuggish appeal. At night, the car’s sinister and flashy side comes to the fore, the beautifully crafted interior lit by blue LEDs and the awesome Meridian surround sound system giving you a full cinematic experience, perfect for cueing up the Get Carter soundtrack. Like the Speakeasy-style bars that are popping up in the world’s coolest cities, with their unmarked doorways, passwords and Hemingway-inspired cocktails, the XJR is a classic that has been remixed for modern times.

The XJR sounds incongruous; a huge luxury barge with the soul of a Fast & Furious street fighter. It sounds like a recipe for disaster, but the result is a super sports saloon with a petrol-pumping heart, a car it’s impossible not to warm to; a no nonsense bruiser that can stay out all night head-banging and still look respectable at the G8 Summit the following morning.