Coachbuilt cars are incredibly rare things these days.

There’s a heap of reasons for this. First, there are almost no modern cars made with a separate chassis capped with non-structural body panels. A separate, load-bearing chassis construction makes it much easier and cheaper to reshape cladding panels because they do not significantly contribute to a car’s stiffness. Which is why coachbuilding was the norm in the early part of the 20th century and was commonplace up to the 1960s.

Modifying a monocoque, stressed bodyshell is much harder but was still relatively feasible until crash regulations made such re-engineering a lot more expensive. As crash requirements and other regulations have become ever more stringent, the viability of one-off or very low-volume models with extensively modified body panels has become prohibitive.

Prohibitive certainly describes the rumoured £20 million cost of Rolls-Royce’s rather beautiful new Boat Tail, of which just three are being built. They are the creation not only of the Rolls-Royce design and engineering departments but also the three owners, who were inspired by the Rolls-Royce Sweptail and the elegant beauty of J-Class yachts. The trio, who did not know each other, met Rolls-Royce people in various parts of the world and were closely involved with the Boat Tail’s creation from start to finish.

The process was aided considerably, explains a Rolls spokesman, by the fact that “they were all people we knew, all very experienced in appointing a Rolls-Royce, and they understood the bandwidth in which we can operate. When ambitions are allowed to run free, this is what motor industry can do.”

While it would be a thrill to see one of this trio if they ever turn up at a concours – and the spokesman assures me that they will be used rather than stored in dehumidified garages, although he does not reveal the countries in which they will reside – the re-emergence of coachbuilt Rolls-Royces is of little relevance to most of us beyond the pleasure of knowing that such things exist.

However, the vehicle architecture Rolls-Royce is using to make such cars possible might just be more exciting to those of us with less voluminous bank accounts. The new Ghost, the Phantom and the Cullinan all share an aluminium spaceframe sub-structure, its design allowing considerable dimensional and design freedom, both for series-produced Rolls-Royces like this trio and for special-build models like the Boat Tail.