The Jaguar C-X75 supercar was created to celebrate 75 years of Jaguar, and was first shown in concept car form at the 2010 Paris motor show.
Back then it was an electric range-extender with a pair of micro-gas turbine engines to charge the batteries.
However, when Jaguar started to develop a production version of the car with the help of the Williams F1 team, it quickly became clear that these turbines wouldn't produce the sort of power required.
Instead, the C-X75 was turned into a plug-in hybrid with a 194bhp electric motor on each axle, along with a turbocharged and supercharged 1.6-litre petrol engine developing 502bhp.
Jaguar claims that this powertrain, combined with the car's lightweight carbonfibre body, gives the C-X75 a 0-60mph time of less than 3.0 seconds and a top speed of more than 200mph.
In spite of that incredible performance, Jaguar claims CO2 emissions of less than 89g/km (about the same as a VW Golf Bluemotion) and a range of up to 37 miles on electric-only power.
The design team behind the C-X75 had to change every exterior surface to turn the concept car into a working prototype that met all the necessary aerodynamic and cooling requirements, yet the end result remains remarkably faithful to the original show car.
What's the 2013 Jaguar C-X75 like to drive?
Small turbocharged engines with big power outputs usually feel flat at low revs, but the C-X75 has a very linear delivery, thanks to the low-down muscle its supercharger and twin electric motors help produce.
True, we only got to drive the car after it had just been recharged, but Jaguar claims that the C-X75 remains a flexible performer when its batteries are running low.
Acceleration is as eye-widening as the 0-60mph time suggests, aided by the car's four-wheel-drive traction. The engine never powers the front wheels directly; instead they're driven by the electric motor on the front axle.
Most of the time 70% of the torque goes to the rear wheels, while the engine will rev to a barely believable 10,300rpm before you have to grab another gear using the automated manual gearbox.
High-rev upshifts are snappy, and downshifts impressively smooth, but upshifts do feel a little clunky at lower speeds.
The prototype car we drove was also fitted with little sound deadening, so you could hear stones pinging off its underside. However, the C-X75's engine note is worthy of a Group B rally car, while the whine from its supercharger only adds to the drama.
The steering is light and precise, too, and the C-X75 stays incredibly flat in corners. That said, it does demand respect; the back of the car will happily slide if you're aggressive with the throttle on the exit.
What's the 2013 Jaguar C-X75 like inside?
The doors open up and out, which looks dramatic, plus they take a large chunk of the sill with them to improve access. However, the C-X75 still isn't a particularly easy car to get in and out of, and the doors are heavy to pull shut.
Things are better once you're inside, because there's space for a couple of six-footers, while forward and over-the-shoulder visibility is decent by the standards of mid-engined supercars. Just don't expect to see much out of the small rear screen.
When it was shown as a concept car, the C-X75 featured a fixed driver's seat and adjustable pedals, but it's just the seat that adjusts on the prototype.
The prototype also has a more conventional dashboard than the concept car, including switchgear that's borrowed from the F-type roadster. Fortunately, it still feels special, thanks to plush materials, heavily cowled instruments and a centre console that's angled towards the driver.
Jaguar says that it has developed new graphics for the C-X75's touch-screen infotainment system, and while these weren't on the prototype, they will be used on more mainstream Jaguars and Land Rovers in the near future.
Should I buy one?
Sadly, you can't. Jaguar had intended to sell the C-X75 for between £800,000 and £1 million. However, last December it cancelled plans to put the car into production, citing higher priorities and the state of the global economy.
Work on the project has been suspended since then, and while Jaguar says you should never say never, it seems unlikely that the C-X75 will ever go beyond the prototype stage.
What it will do is influence future mainstream Jaguars. These will be offered with powerful and efficient small-capacity engines albeit less extreme ones than the C-X75's 1.6 plus the company is continuing to develop both hybrid and turbine technology.
Even the C-X75's lightweight carbonfibre panels could reappear, although they will be used only on high-end cars for the foreseeable future, because carbon currently costs between three and four times as much as aluminium.
Engine size Supercharged 1.6-litre turbo petrol, plus twin electric motors
Power More than 850bhp
Torque More than 738lb ft
0-60mph Under 3.0 seconds
Top speed 220mph (Jaguar estimate)
Fuel economy n/a
CO2 emissions Less than 89g/km