Got a little bit more for you. The Westward Airways Islander link started on 25 June 1969 but the exact date it finished I know not. When it started it used to slot in visually behind ILS traffic. That was before the days of vortex wake and such a procedure now would cause intolerable delays. You may be interested to know that in 1969 there were just 168 Boeing 707 movements at Heathrow whilst there were 2570 by Britten Norman Islanders.
This and the previous information came from the book "Heathrow ATC, the first 50 years".