Managed to locate British Civil Aircraft Vols I -III (simples, look on bookshelves - had thought they were currently in a box with most of my other aviation books due to decorating!) and gleaned the following: the Grasshopper 1 was developed for Rotorcraft Ltd by Servotec Ltd. The Grasshopper IIIs were built by Cierva as the CR LTH-1 Grasshopper 3 in conjunction with with Servo-Tec Ltd.
Would have been Farnborough 1970 - 'WRP and 'XFM both flew in 1969 apparently.