This is the Gillie, a Rootes Group-commissioned prototype for a Mini Moke-type vehicle equipped for off-road use.
It was actually developed by Tilling Stevens in Kent.
It dates from 1970, and apparently only 1 was built.
It was whisked off to Lord Rootes's estate after first being demonstrated to the Rootes brothers - never to be seen again by its developers!
It showed up on ebay in 2006 so still exists somewhere.