This remarkable, flying-sauncer-shaped car, known officially as Alien, makes its debut in the fourth episode of ‘Invasion of the Dinosaurs,’ and has been made specifically for Jon Pertwee by custom-car specialist Peter Farries of Nottingham. The two men first meet in January 1973 in the Midlands, when Jon opens a new Ford Main Dealers. Peter is there with his own astonishing green-and-black custom Black Widow. So impressed is gadget-loving Jon that he commissions Peter to build a 'special’ for the Doctor — but, he says it has to be legal for driving on public roads (which, of course, Bessie isn’t) and it has to look like something from outer space.
The result is Alien — a fourteen-foot fibre-glass-hulled vehicle sitting on an anchor-shaped chassis with three wheels (which are hidden from view by an eight-inch rubber skirt to give the Whomobile the illusion of being a hovercraft). The Chrysler Imp 975 cc engine can propel the 14 cwt car to a top speed of 105 mph, and its special electronics system of 44 flashing lights plus mock-up computer, telephone, television and stereo give it a truly futuristic look. When Jon first presents the Whomobile at the studio there is amazement and consternation among all the other actors and crew! Amusingly, the Road Licensing Department classify Alien as an 'Invalid Tricycle.’ […] As Jon Pertwee’s property, the Whomobile leaves when he departs the series, but it has since been seen at fêtes and special openings.