It wasn’t so very many years ago that the thought of putting a diesel in a luxury car would have had people choking on their canapés but times, they are a changing, and so it was that I found myself behind the wheel of an oil-burning Bentley Bentayga.

That’s right, the luxury car maker has slipped its first diesel engine – technically it’s Audi’s but, according to Bentley’s engineers, it’s been recalibrated for the Bentayga– diesel engine beneath the bonnet of its first SUV.

Two firsts for the, not inexpensive, price of one then.

Power – all 429bhp – comes from a 4.0-litre twin turbocharged V8 with a 48V compressor. Perhaps more impressive is the 900Nm of torque that’s available from just 1,000rpm, or as near as makes no difference to idle. That power figure matches the W12 model but it delivers all that turning force significantly earlier.

Drive is sent to all four wheels through an eight-speed automatic gearbox.

Before we worry about whether the inclusion of a diesel-powered Bentayga in the, admittedly compact, range of models is a wise move let’s focus on the rest of the car and what makes a Bentley, regardless of its power source, special.

First of all you get that immediately identifiable front end. It’s imposing, instantly recognisable and the trademark twin light clusters and huge mesh grille make the transition from Bentley's saloon cars to its big SUV very comfortably.

The view from the front is, arguably, the best one because, as I noted when I drove the 12-cylinder version, the design does, for me, lack a little fluidity.

The front, the sides, the back, all feel a little disparate as though, in a bid to make the Bentayga as much of a Bentley as possible, the designers were more concerned with adding as many familiar design cues as possible – both the Mulsanne and Continental GT’s make significant contributions here – and less about how they were going to combine them seamlessly.

It isn’t just the engine that the Bentayga borrows from the Q7, it also sits on the same platform with a wheelbase that’s just 1mm longer. In every other direction, however, the Bentayga is much bigger at 5130mm long, 1998mm wide (2224mm including the mirrors) and 1742mm tall.

The cabin is as well appointed as you’d expect in a car that would attract a council tax bill of approaching £2,000 a year in the Garden of England. Open the door and the first thing that strikes you is the rich, warm scent of leather. Hardly surprising as the cabin is drowning in it. From the window sills to the door panels, the swooping asymmetrical dashboard to the transmission tunnel, the steering wheel to the seats, there is absolutely oodles of the stuff. Anything that isn’t wrapped in leather is covered in a lustrous, deliciously finished wood veneer.

Housed in the instrument binnacle is a set of analogue instruments that flank a colour LCD screen that can display navigation guidance and media information as well as trip details and more.

A head-up display is optional, as is night vision, both of which I would recommend, and not just because they’re cool either. There’s nothing better than receiving important information – speed and sat nav directions for example – in your line of sight. It really is magic.

The seats are beautifully sculpted and luxuriously comfortable. They, and the steering wheel, are electrically adjustable and, once you’ve got everything just as you want it there are few experiences to rival gazing down on the world passing you by in serene silence from the lavish confines of the Bentayga’s cabin.

If you would rather be driven than drive you’ll find accommodation in the back just as generous. The standard split-folding rear bench accommodates three but there is the option to choose a strict four-seater with a raised console-equipped transmission tunnel and reclining seats with massage function.

Perhaps, most importantly, there’s ample for room for adults, even of larger proportions, to get comfortable. All that luxury would be wasted otherwise.

Compared to cutting edge multimedia systems found in some cars the 8in colour touchscreen does appear a little dated but, in isolation, it suits the character of the cabin. The screen is crisp, clear and easy to use for the most part too, although one glaring omission is the lack of an alternative input method to touch. It’s fine when you’re stationary but poking at the screen while on the move can, literally, be a bit hit and miss.

Unless you want to save some cash for a little runaround it’s probably worth splashing out the £6,300 it costs to install the Naim for Bentley audio system. Simply because its brilliant.

Now, back to the main talking point: That diesel.

First it’s important to note that, without being told, no one sitting inside the car would have the slightest notion that this is a diesel-powered automobile. The refinement, the noise insulation, the overwhelming sensation of isolation from the outside world remains. That, in itself, is quite an achievement because every other car that I’ve driven has always given me some clue as to what’s beneath the bonnet. Not the Bentayga.

That's largely down to the huge amount of effort that has gone into concealing the origins of the Bentayga's performance. The engine bay has been fitted with more soundproofing than the W12 version, the sound of the V8's combustion has been dialled down a little and the motor sits on intelligent engine mounts.

Start the engine and listen hard. I mean really hard. There it is, a deep, distant rumble as the V8 discreetly ticks over. Press down on the throttle a little, then a little more and while the volume rises, it’s never much more than a muted burble, never anything more than the distinct, but instantly recognisable, mumblings of a V8.

Striving for refinement hasn’t compromised the motor’s performance in any way. It will reach 60mph in a brain-scrambling 4.6 seconds while its top speed, where legal of course, is 168mph. Clearly this car is no slouch.

Like its 12-cylinder petrol-powered sibling, however, it’s the way that performance is delivered that really sets pulses racing, spines shivering and palms sweating. From a standing start the Bentayga will sit back on its haunches before catapulting you towards the horizon at an improbable pace, gathering speed with effortless grace but brutal intent.

Shut your eyes – not if you’re driving, obviously – and you’d have very little notion about the velocity you were hurtling along at. The only clue is the tiniest hint of wind noise.

It’s a juxtaposition. Both a beauty and a beast. Opposing forces combine to confuse the senses, to reconfigure and redefine expectations. The Bentayga diesel’s searing pace and phenomenal power provides a stark contrast to its cosseting, unflustered ride and exceptional refinement.

Forty per cent of the power is sent to front wheels and the remainder to the rear and, should your journey necessitate a trip into the wilderness, you’ll find that a combination of variable ride height, the sophisticated four-wheel-drive system and hill descent control ensures that the Bentayga is a seriously capable off-roader.

The adaptive air suspension and active anti roll systems work in unison to shrug off low-frequency imperfections and give the Bentayga a degree of composure that you wouldn’t normally associate with a car so tall, so heavy and so geared towards comfort.

You can select your preferred driving mode using the rotary dial on the transmission tunnel. Some intended for snow, sand and wet grass and others – Comfort, Sport, Custom and Bentley – provide preset options for everyday driving.

Bentley mode configures the car to the engineers’ specification but, while it takes the effort out of setting up the car yourself, doing just that allows you to dial out most of the compromises that the other modes force you to make. Comfort mode, for example, sacrifices high-speed body control for a smoother ride.

Sport mode would appear to be an unnecessary inclusion given the nonchalance with which the Bentayga conducts itself but should you wish to put its athleticism to the test you’ll find that it responds deceptively rapidly to steering inputs while remaining remarkably flat as it changes trajectory.

That is in no small part thanks to the active anti roll bars which are 48V resistive units which, when Sport mode is selected, remain relaxed under normal driving but tighten up when required to reduce roll and improve responsiveness.

The first comparison you'd probably make is with Range Rover's SV Autobiography arguing, I imagine, that it'll be less expensive and, on that score, you'd be wrong. The Bentayga undercuts Land Rover's finest by a considerable margin. Admittedly, as good as Crewe's SUV is, it doesn't quite have the off-road credentials as its rival, but would you really put that to the test?

What about the Q7, with which the Bentayga shares both its platform and its engine. Surely that offers better value for money?

It's true that while the basic Bentayga appears to offer luxury motoring at a reasonable price, that can quickly change once you start ticking boxes on the extensive options list.

Then there is, perhaps, the most fundamental question of all: Would someone who could afford to spend approaching one fifth of a million pounds on a fully-loaded Bentayga really consider buying one with a diesel under the bonnet?

Maybe they wouldn’t, but maybe they should, because in doing so they’ll snare themselves arguably one of the finest luxury limousines on the planet. It’s almost as fast as its W12-engined sibling, as equally refined, returns about 36mpg (if you can resist the urge to keep asking it to apparently break every law in physics, something that was beyond me during my week with it), plus you’d save yourself enough money to buy that swimming pool you’ve always promised yourself.

Bentley Bentayga diesel

Price: £135,800

Engine: 4.0-litre V8 diesel

Transmission: Eight-speed automatic driving all four wheels

Max power: 429bhp

Max torque: 900Nm

Max speed: 168mph

Acceleration (0-62mph): 4.6sec

Combined: 35.8mpg

Emissions (CO2): 210g/km

For more information visit www.kent.bentleymotors.com