“The first question we always ask is if there’s a donor platform in mind, because that’s the really expensive part of any vehicle design,” says Envisage engineering director Paul Arkesden (a former McLaren project manager). “If we can carry over an existing car, you’re more than halfway through.” Jaguar XKR and BMW 7-series are popular choices.

It’s also important to know what the customer wants the car to do.

A 1960s or ’70s style with modern performance and reliability is a common wish. Most customers will have a design in mind – but if they don’t, then the designers will work with them to create it. Yet it has to work with the donor platform.

“We take the donor car down to the basic structure, the parts we’re going to use; that’s quite a bit of the underbody, the suspension, the engine… We scan it to get a mechanical layout – the wheelbase, radiator position, engine location, suspension mounts – and graft the customer’s design over the top.

“At the end of six months you should have a style that will fit over the donor platform selected,” says Chief Engineer Craig Bonham. This is the point at which a customer can have more input, sitting in the VR (virtual reality) studio to finesse the design, and looking at mood boards for colour, material, and material finishes.

Alongside, engineers will produce a DVP (design verification plan) to assess the durability, performance, and handling of the car. Safety and adherence to regulations – external and internal radii, the position of lights, visibility of turn signals – is designed in, and the car’s structure is calculated using CAE (computer-aided engineering) systems.

“Once we’ve got the package and we’ve got the design, we convert the data to a powerwall and project the car onto the screen, to ensure the customer is happy,” explains Arkesden.

The next stage is making press tools, machining them from solid aluminium. Bodies are usually made in aluminium, although steel and carbon fibre are possible as well.

At this stage, the customer will often visit again to see the panels being made, and may even take a turn on the English wheel rolling sheets of aluminium. Once the bare body-in-white has been signed off by the engineers and the customer, it goes to paint, often using bespoke colours created from scratch.

And then it’s trim followed by five or six days of testing – Envisage uses nearby MIRA – covering around one thousand miles to check ride, handling, and durability. If a donor platform has been used, then the car will retain that identity, and it will go through an IVA process to confirm it’s safe and legal. Then the car will be ready for final preparation and handover to the customer.

The price? For a one-off, “expect it to have six zeros,” says Arkesden.