When I was a kid, I had a friend who used to collect things from a nearby army training ground. Spent machine gun rounds, the occasional flare, that kind of thing.

That meant he spent most of his time looking like some kind of well tooled-up magpie, but his rather questionable predilection for spent artillery required an increasingly inventive selection of places to hide his semi-lethal trinkets from his parents who, if they’d known, would have reached for the yellow pages faster than you could say ‘bomb disposal squad’.

I have a suspicion my friend now works for Jaguar, because someone in their engineering department clearly felt the best place to hide a weapons-grade supercharged 5.0-litre V8 was under the bonnet of an otherwise innocuous-looking estate car.

From the outside, the XFR-S Sportbrake offers few clues that behind the enlarged air intakes lies a lump of unexploded ordnance. Specify a muted exterior colour such as a classy metallic grey, and even a passing NATO weapons inspector would be hard pressed to tell the R-S apart from a diesel XF with a few tasty options.

Those in the know, however, will readily spot the 380mm brake discs and red calipers peeking out from behind the 20-inch alloy wheels, while the modest carbon fibre additions to the front and rear bumpers join with the quad-pipe exhaust system to give more of a clue as to what lies beneath.

The clues mount up once you climb inside, particularly once you clock the desperately appealing contrast piping and stitching and the equally attractive carbon weave material on the seats and doors.

Beyond a couple of modest R-S logos on the steering wheel and aluminium dash trim, the cabin is largely XF business as usual, and that’s no bad thing because that means seats that feature adjustment in every direction you can think of (plus inflatable side bolsters and lumbar support), straight-forward controls for the climate and audio systems, and a welcome lack of gimmicky iDrive-style controllers.

Instead, the minor functions are presided over by a centre-mounted touch-screen that also calls itself home to a rather special 825W Meridian surround sound system. It’s loud enough to set off land mines within a 50 foot radius and remains deliciously distortion-free even at ear drum-perforating volume levels, although to our abused ears the Mark Levinson system employed by Lexus offers slightly tighter bass control.

The rest of the system’s functions work well, with the satnav offering full UK post code capability, although it can feel a touch laggy at times, and some of the graphics aren’t quite up to the standards of the high-res systems in the competition.

Rear seat passengers will find the Sportbrake offers slightly more headroom than its saloon brethren, although whoever draws the short straw and finds themselves in the middle seat will have to contend with the high transmission tunnel.

Cargo space is a useful if not desperately commodious 550 litres with the seats in place, although it scores highly with a handy selection of load hooks, storage compartments, and adjustable load rails to help keep your belongings restrained – and you’re going to need them.

The rear seats fold easily thanks to a pair of levers mounted in the boot walls, and in this configuration there’s 1,675 litres of space on offer.

Access to this space is easy, thanks to a low and wide load sill, our only complaint being that while you can open the power tailgate either from the keyfob or via a button in the cabin, to close it you have to use the button on the tailgate itself.

With the practicalities out of the way, it’s time to talk about the small invasion force that’s hiding under the bonnet.

Lift the lid and you’ll find yourself staring at a supercharged 5.0-litre V8 that rumbles away to the tune of 542hp and 680Nm of torque. Mated to an eight-speed ZF automatic transmission, it can thunder its way from 0-60mph in just 4.6 seconds and keep on trucking until its electronically-limited 186mph top speed. Not even Hans Blix could hide this level of performance.

Press the start button and the cat is well and truly propelled out of the proverbial bag as the V8 auto-revs into life with a crackle that sounds like small arms fire. Give the throttle too many prods early in the morning and you might find your neighbours start a campaign to make you the subject of a UN resolution.

Inside the cabin, things are more subdued, however. While the exhaust pops and crackles like a ‘60s racer, particularly on over-run, much of the XF’s vocal performance seems aimed at those following in your sonic wake. Jaguar’s engineers have done an excellent job of tuning the sound of this beast, it’s just that if I’d spent over eighty grand on one, I’d like to be the one getting the benefit from all that work.

There’s no masking the performance available from that engine, however. Plant your foot in the carpet and everything around you instantly becomes history.

The ease with which that happens is what makes the XFR-S so potent, and much of the praise for this should be laid at the feet of the excellent automatic gearbox.

Leave it in Drive and it’ll happily take care of everything for you, its ability to downshift multiple gears at once giving the XF overtaking abilities to rival most motorbikes.

It’ll recognise when you’re tackling a series of overtakes in quick succession and will hold on to lower gears automatically, and it’ll do the same for corners, too.

Rarely was there a moment during our time with it that it made a poor choice of gear, but even if it did the speed with which it reacts to changing circumstances means that would never be an issue anyway.

If you prefer a little extra driver involvement you need only pull back on the left-hand steering wheel-mounted paddle to swap down a cog or two, with the engine management system automatically blipping the throttle to match engine speed to the new ratio.

Once over-ridden, some transmissions will revert to fully automatic mode after a set period of time, but the unit in the XF is smart enough to leave you in your chosen gear for as long as you might need it – longer if you’re tackling a series of corners, for instance – and will only change up once it’s clear you’ve finished cavorting about. Alternatively, you need only hold the right-hand paddle to revert to auto mode yourself.

If you prefer full manual control, push and twist the gear knob into the Sport position. By default, the transmission will automatically drop down a gear or two ready for a rapid response, and in this mode 7th and 8th gears aren’t normally selectable (although you can get them by holding the right-hand paddle).

In Sport, you get the final say as to which gear you’re in, and I have to say, it’s probably the fastest-responding automatic gearbox I’ve driven, with new ratios engaging practically immediately.

This rapid response helps makes a series of corners even more enjoyable, and it’s here that you’ll discover the handling is more than equal to the task.

Body control is incredibly tight, turn-in is flat and crisp, and its natural state through a corner is remarkably well balanced for a car this size – until you give it an intentional bootful, of course, and hang the rear end out, something that’s tantalisingly easy to do even without engaging dynamic mode.

The XFR-S’s party trick, though, is that this level of performance is all wrapped up in a huge blanket of civility. For all its taught body control, the ride is incredibly comfortable. Whereas the German competition gives things a harder edge that can become tiresome, the Jag gives you genuine all-day comfort and a ride that wouldn’t upset your mother.

Rarely does a car come along that offers not just this level of space and performance, but also a matching degree of refinement and a sense of theatre.

Ok, so it’s not cheap – you’ll need to write a cheque for £82,495 to get one, and it’s got a bit of a drink problem, too, recording an average during our testing of just 19mpg. But it’s a bit like your favourite aunt who drinks too much sherry at Christmas – somehow you just can’t stop yourself from topping up her glass.

Rather than start an arms race with the German competition, Jaguar instead created something a little more refined. Perhaps even tasteful. Hardly the place you’d expect to find a weapons cache, then. But my God, does it pack an explosive punch.

Entry-level Price £82,495 Price as tested £84,245
Engine Supercharged V8, 5000cc Transmission Eight-speed auto
Power 542hp @ 6,500rpm Torque 680Nm @ 2,5-5,500rpm
0-60 4.6 secs Top speed 186 mph (limited)
Economy 22.2 mpg CO2 297 g/km
Dimensions 4966 x 1939 x 1511 (LWH) Kerb Weight 1967 kg

Alex Kefford

Editor

Freelance journalist, ex-offroad driving instructor and long distance road-tripper. If you have any questions about this piece, feel free to hit me up on Twitter.