The Mulsanne is all a flagship luxury car should be

There is something surreal about this mental picture. The car in it has normal proportions but its occupants' heads seem too small.

Now I'm in this picture, walking from one end of the car to the other, and it's taking longer than expected. Next, I'm in the driving seat and, on a road somewhere on the Scottish/English borders, enormous quantities of air are being pummelled aside as the car hurtles along.

Massive forces are at work here. The torque – the ability to twist driveshafts – of the engine is so huge that those driveshafts must surely soon resemble giant drill bits. The road gets narrower; will this outsize car fit the gap? It does, but were its steering not so accurate there would have been less certainty that the door mirrors would stay unscathed.

Larger than life. That's the new Bentley Mulsanne, heir to the tradition of slightly mad automotive aristocrats that grew from the notion of turbocharging what was otherwise a differently-badged Rolls-Royce. That Rolls/Bentley connection has long gone, and nowadays the UK's two grandest luxury brands are rivals.

Under Volkswagen's ownership, Bentley continued to make the old models with their 6.75-litre V8 engines alongside the new, smaller Continental range, even updating them from time to time. The last time we reported on the Arnage, as the venerable saloon was latterly named, we found it a lovable dinosaur.

Knowledge that Rolls-Royce was developing its "smaller" – Arnage-sized, in fact – Ghost model must have concentrated minds, because it meant that for the first time in history, Rolls-Royce and Bentley would be in direct competition. We have tested the Ghost and found it the most sporting, most driver-pleasing Rolls-Royce in living memory. No previous Rolls has ventured so far into the territory Bentley hitherto called its own.

Here, then, is the new £220,000 Bentley Mulsanne. Once again designed, engineered and built entirely at the Crewe, Cheshire factory, the Mulsanne is an all-new car even if the basic architecture of its twin-turbo V8 engine remains that of its 50-year-old predecessor. That means the engine still has just one camshaft, but now its timing can be altered to the great benefit of efficiency. Some design features of the old engine – short exhaust ports, wedge-shaped combustion chambers – have serendipitously turned out to be good for low emissions, so they remain. What is very new, though, is that the engine can switch off four cylinders when being driven gently, turning the Bentley engine into a 3,375cc V4.

You can't hear or feel the change in cylinder-count. Nor can you readily perceive the shifts in the new eight-speed automatic gearbox. All you feel is the wall of propulsive energy, all 512bhp and 752lb/ft of it, while all you hear is a distant, deep rumble if you goad the beast. At idle the engine is all but inaudible, and even when roused it seldom ventures beyond 4,000rpm even though 62mph can be reached in 5.3 seconds and there's the potential to reach an extraordinary 184mph.

Unlike the Ghost, which you simply drive, the Mulsanne has a Sport mode to enhance the transmission's alertness, plus a control to set the air suspension in one of four modes.

Driving the Mulsanne with the vigour its sporting ancestry might encourage requires a degree of chutzpah. It occupies much road space, you're always aware of the vast momentum and its presence might intimidate others. You can try to be discreet, but the proud prow and the giant headlights make it hard. This big Bentley is amazingly agile for what it is, though, and you feel much more at one with it than you would ever feel in the old Arnage. It helps that you sit a little lower, in a cabin just as beautifully created from hand-wrought wood and leather but rather better organised and exquisitely detailed.

Naturally there are myriad finishes and colour schemes from which to choose, but common to all combinations are lovely black-glass switches, the usual chromed-metal air vents, and a stupendous sound system complete with a leather-lined iPod drawer. The Mulsanne is a modern interpretation of the Bentley ideal, its shape immediately recognisable but created with ultra-modern technology.

The Mulsanne is everything a modern flagship Bentley should be. Trouble is, so is the Rolls-Royce Ghost, which may be less completely British with its smattering of BMW components but is somehow more progressive in its design and purer in its concept. Personally, I'd opt for the Rolls-Royce. But if you disagree, I understand entirely.

The Rivals

Aston Martin Rapide: £139,950

Based on a stretched DB9, blends luxury and pace but not the space of the Mulsanne. Only in this company could the 470bhp V12 seem lacking.

Mercedes-Benz S65 AMG L: £153,342

AMG tag means it's a tuned-up S-class, but it still oozes luxury and civility. It just happens to have a 612bhp turbo V12 too.

Rolls-Royce Ghost: £195,840

More power than Mulsanne from twin-turbo V12, less torque, better fuel economy. Satisfying to drive, has intriguing rear-hinged rear doors.

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