That car is "The Beast", a creation by John Dodd. Looking like the combination of the Family Truckster, a Rolls-Royce Carmargue and possibly some sort of Shooting Brake version of a late '70s Camaro, this 19 foot monster hid a very large secret - a 27 Litre Rolls-Royce Merlin airplane engine.
It originally sported a Rolls-Royce grille (pictured above in a 3D represenation), but now sports the stylized "JD" seen below after legal threats from Rolls-Royce.
Regardless of how it looks however, the fact that it even exists and works is impressive. Follow these links for first hand accounts of driving the monster:
http://www.evo.co.uk/features/features/228789/the_beast.html
http://www.youtube.com/watch?v=OxMxFE37Sxw
*EDIT* - here's a bonus pic of the original body, which was destroyed in a fire. Carries a similar Rolls-Royce air, but in a body that looks like a stretched Capri.