You might think that falling asleep on the job is a tad inadvisable for a car tester. But every so often a car comes along where nodding off while travelling at speed is a vital part of the evaluation process.

I’ve always found the rate at which oblivion descends is one of the very best yardsticks by which to judge a luxury vehicle. I’m a nervous passenger at the best of times and it is a rare car indeed that is quiet, comfortable and soothing enough for me to surrender myself into the arms of Morpheus.

But I had not been in the back of this new £115,000 Bentley Continental Flying Spur for more than five minutes before I felt my muscles relax and my eyelids grow heavy. It had passed its first test.

The Flying Spur, named after a much-loved Bentley from the 1950s, looks like a stretched four-door version of the Continental GT — because that’s precisely what it is.

It has the same 553bhp twin-turbo W12 engine sourced from its Volkswagen parent and the same gearbox, suspension and brakes.

It has had an extra 300mm of length inserted between its wheels to provide what turns out to be more than adequate rear legroom and a slightly awkward boot grafted onto the back of the car in place of the GT’s rather more elegant and integrated rear end.

Its aim is to be a high-end luxury limousine that also offers genuinely sporting responses: a car you can go to work in during the week and play in at the weekend. And those of you who thought that was precisely the job of the £160,000-£180,000 Arnage range are not alone.

Quite what effect this new saloon will have on its charming but aged — not to mention slower and more expensive — big brother remains to be seen, but suffice it to say for now that Bentley is already peddling the Arnage’s rarity as a selling point.

By contrast, the Flying Spur is expected to sell in such large quantities Bentley is likely to have to build it not only in the Crewe factory — where all Bentleys have been assembled since 1946 — but also in Dresden. In doing so the car maker will utilise some of the capacity made available by the painfully slow-selling VW Phaeton, a vehicle that shares many of the Bentley’s underpinnings.

For the most part this success will be deserved, not least because the design works even better as a saloon than as a sporting coupé. Indeed, the two main criticisms you can point at the Continental GT — that it is too heavy and its engine lacks character — are almost a benefit in a luxury saloon.

The Flying Spur weighs about 2½ tons, as much as two family hatchbacks and enough to steamroller its way over most bumps and provide ride quality that, while not quite as good as a Mercedes-Benz S-class, is nevertheless smooth, compliant and fully in keeping with its luxury aspirations. The engine is also more suited to the saloon treatment: in such a car it is easier to forgive the rather anodyne roar and stately performance.

Just occasionally, however, you’ll want to remind yourself that this car is more powerful than any Ferrari currently on the market and it takes just one flex of the foot to do it. The Flying Spur’s 0-60mph time of 4.9sec looks impressive enough for such a large car on paper, but you need to experience it for real to appreciate the rare majesty with which this mobile mansion will throw itself down the road.

Ultimately it will do 195mph, making it the world’s fastest saloon, if only because Mercedes will not allow its £147,935 612bhp S65 AMG within 50mph of its true 205mph potential.

But despite the power, the speed and the Bentley badge, the Flying Spur is no sports car. If you point it up the side of a mountain and turn off the traction control, it will make a brave attempt at handling hairpins and tight turns but its heart is clearly not in it. But belting down an autostrada, sweeping from curve to curve with absolute security, it felt in its element. The combination of four-wheel drive and iron-fisted body control made it as comfortable in that challenging environment as any other car in my experience.

Objectively, however, it remains hard to make a case for the Flying Spur over, say, a Mercedes S600, which is not only potentially as fast but undoubtedly quieter, a better ride, as spacious in the back and more than £20,000 cheaper. All it lacks are the Bentley’s more personal qualities: the ambience of its immaculately presented wood-and-leather interior and the sheer sense of occasion that accompanies even the shortest drive.

Ultimately an S-class — however effective it is (and I rate it still as the best mass-produced luxury car in the world) — remains a tool for doing a specific job. You can’t get emotional about an S-class and it won’t make you feel privileged just to be on board. These are things Bentleys have always done, and the cleverest thing about the Flying Spur is that these values have been only slightly diluted, despite it being designed in the virtual world and manufactured largely in an automated one.

The Flying Spur is far from perfect but if you want a modern, spacious limousine that goes like hell while making you feel like the multi-millionaire you undoubtedly are, the Flying Spur is hard to beat.

VITAL STATISTICS

Model Bentley Continental Flying Spur
Engine type W12, 5998cc
Power/Torque 553bhp @ 6100rpm / 479 lb ft @ 1600rpm
Transmission Six-speed sequential
Fuel/CO2 16mpg (combined cycle) / 423g/km
Performance 0-62mph: 4.9sec / Top speed 195mph
Price £115,000
Verdict Successful fusion of old world charm and modern technology
Rating 4/5

THE OPPOSITION

Model Mercedes S65 AMG £147,935
For Awesome power, discreet presence, very civilised
Against Getting old, handling does not match performance

Model BMW 760Li £80,980
For The best-handling big limo, smooth V12 engine
Against Hideous depreciation, annoying iDrive system