What the hell is that?!
It's commonly referred to as "The Beast".
The chassis and engine were indeed Paul Jameson's work, as integerspin pointed out.
John Dodd (Paul Dodd is his son and restored the car some time ago) was a genius with automatic transmissions, so he was asked to build a transmission that could handle the power of the engine.
He ended up buying the rolling chassis and turning it into a car.
As for the engine itself, it is still unclear if it's a Merlin or a Meteor. Jameson says it's a Meteor, Dodd says it's a Merlin.
It has two spark plugs per cylinder, which is an aviation requirement and classifies it as a Merlin. As far as I can tell, the Meteor has one plug per cylinder. Then again it has a wet sump like a Meteor.
It's probably a bit of a Franken-build, a Meteor lower with Merlin heads. Dodd reckons it has "about a thousand horsepower at 2500 RPM".
At first it had a normal body (as far as anything with a 10-foot bonnet can be considered normal), with a Rolls Royce grille and the roof of a Capri. In this guise it was mainly used for shows and drag races while he worked on the cooling and reliability.
A fire in the garage destroyed the car, but the engine and chassis remained intact. Dodd then had that station wagon body built, again with a Rolls Royce grille.
He often rode it on the autobahns, which had quite a few supercar owners scratching their heads because they would be going flat-out in their 911s, Ferrari Daytonas or Lambo Miuras, only to be passed by a gigantic station wagon.
Legend has it that the polizei asked Rolls Royce to stop testing their new prototype on the autobahns, because although there were no speed limits there, speeds of over 200MPH were considered anti-social.
TBH I doubt this is true. John Dodd himself once said that he preferred to keep the speed below 180MPH because he was too worried about the (enormous) flywheel. Mind you, the car is geared for 210+ MPH and will reach that without breaking a sweat, so it's theoretically possible.
All that's certain is that Rolls Royce did eventually sue Dodd and wanted the grille removed. Unfortunately he lost the case and both Dodd and the car disappeared overnight.
Years turned into decades and The Beast was almost forgotten, but some people were still searching. Eventually a reporter tracked him down in Spain.
Funnily enough, The Beast is still registered in the UK and despite the court case the DVLA still lists it as a Rolls Royce. At least that's the manufacturer name you need to enter if you want to look it up in their database.