thanks for your rapid replies.
i had success this morning after laying awake many hours thinking it through.
First i checked all the wiring
and tested for voltage drops/leaks. All seemed ok, but i'm no expert on electronics
. ( Have Nigel Calder's book , and it helps a lot)
Then i reasoned...we can get the solenoid to click, and the starter to whir, but seperately. Why not try both at the same time?
So I had my girlfriend hold the satrt button while i cabled directly from the ignition terminal to the battery. Starter whirred, then grinded a little. Stop.
Then i just tried the cable direct to the battery again from ignition post and the engine turned over and started. Great reflief.
I'm thinking, maybe the solenoid still isn't properly engaging the lever to the starter motor, but it is just enough.
So i might need an engine room switch by the sounds of it.