Rolls-Royce bespoke Sweptail takes to Goodwood hillclimb

That customer worked directly with the firm’s design department, which is led by Giles Taylor, the brand’s director of design.

“Sweptail is the automotive equivalent of Haute Couture,” said Taylor. “It is a Rolls-Royce designed and hand-tailored to fit a specific customer.”

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The price of Sweptail was not disclosed (perhaps predictably), with Müller-Otvös calling reports of a £10 million cost "speculation." But he added: "I can tell you it was substantially expensive, substantially expensive. You can easily write this is probably the most expensive new car ever.

"We costed every single process with him up front, so he knew what every single decision would be and what the price would be. It was a very fair gentlemen's agreement, so he knew what would happen. There was no fixed price. There was a dream, not a fixed price. The dream came true - and that costs a bit of money."

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Müller-Otvös said that aside from working with the customer to ensure Sweptail retained the feel of a Rolls-Royce while also being a one-off, the only real restrictions came from Europan road safety rules. He explained: "We had some moments which came to certain design lines which might have interfered with, say, how airbags were deployed. Then you are crossing lines which means you fail to comply with legal requirements.

"We knew this car needed homologation for European markets, because he wants to drive the car here, so there are certain boundaries that you cannot cross. But he was fully understanding of that. We had points when he wanted to stretch us in certain directions and we had to say ‘no, that’s not possible.’"

Rolls-Royce Sweptail exterior design

The front of Sweptail features the traditional Rolls-Royce front grille, although it is the largest version ever constructed. The grille is milled from solid aluminium and polished by hand to a mirror finish.

The rear of the car is tapered with a raked stern, a design nod intended to evoke racing yachts. The rear brake light is housed in a ‘bullet-tip’.

At the side, the bodywork has been designed to wrap under the car with no visible boundary, which is designed to mimic the hull of a yacht.

The most notable exterior feature is the large panoramic glass roof, which Rolls-Royce says is one of the largest and most complex ever produced for a car.

Discussing how the design developed, Taylor told Autocar: "We discussed what we could do with the customer, how the collaboration would work. We talked about the fact it would be based on the Phantom Coupe, would have two seats and he wanted a glass roof, and finally he wanted the fast-back gesture. We took it from there. The final execution grew into a vision we jointly conceived.

"It’s a Rolls-Royce, that’s the key thing from my point of view. We delivered a unique and extraordinary one-off car, but it had to be a Rolls-Royce. It had to conjure the magic of the heritage."

Inside the Rolls-Royce Sweptail

The interior is Sweptail was designed to be clean and minimalist. The customer chose a two-seater, according to Rolls-Royce, to exude “the romance of travel for its own sake”, and place the car “in the grand pantheon of the world’s great intercontinental tourers.”

Rolls-Royce has kept controls to a minimum on the dashboard, with only control on the dashboard. The clock is embedded into the fascia, with the hour marks for that, along with the faces, numbers and hands on the instrument dials, machined from titanium.

Much of the interior trim is crafted from Macassar Ebony and Paldao wood, with Moccassin and Dark Spice leather trim on the seats, armrests and dashboard top.

In place of the rear seats is a vast expanse of wood that has been crafted into a mid-shelf with an illuminated glass lip. There is also a hat shelf, which sits under the rear opening backlight.