Well, after a couple of hours poking about and finding nothing!! Except that the immobiliser light goes out whichever on the multiplugs is removed from the back of the dashboard assembly so signal wire on one and return earth in the other I suspect. The assemby itself comes apart reasonably, once inside it's a single PCB supported on the back of the switches with a ribon cable to the warning light strip. I can no longer recreate the effect with my fingers behind the dash, but I still get a flickering when driving. Moreover, standing on the running board and rocking the car caused the light to go on solidly. So I am wondering if Harald was right and rocking the car like that causes a pool of water in the ECU casing to splash about.
The ECU is in a steel case inside the car attached to the top of the footwell. It's attached by 4 security type hex bolts which I don't have. You can't get to any of it's plugs and pulling the loom about makes no difference. I guess I need to take a trip out and get some tools.
