As unlikely as it seems, "Jumping Jeeps" was the search term that was the magic key to the magic door.
This vehicle was Handley Page's submission for the British Military's "Project Prodigal" . . . an attempt to produce a jeep-sized vehicle that could jump or hop a fairly considerable distance on the battlefield, through the use of either ducted fans, jet assist, or a combination of both (depending on the company). Short Brothers also submitted design proposals. The puzzle vehicle is Handley Page's "Model B" design - their "Model A" appeared to use a rotor system to provide lift. All of this silliness appears to have taken place in the late 1950s-early 1960s. There is actually a decent amount of material on the internet about it.