Does terminal 4 actually have a screw and clamp - the drawings in the instructions don't show them?
Yes. Forgot to mention. Only the terminal number 4 is shown on the diagrams, though my frost stat also has a screw and clamp on T4 too.
If there is a screw and clamp and no continuity to any other terminal, your wiring scheme would work.
Thanks very much for your prompt and helpful response. As usual Mr Hailsham