Thanks Avo for your continued interest.
If I touch and hold the sensor wire, it will stay on the dimmest setting, it only changes when released and touched again….. (as it should).
Once connected to the base (or any other metal part of the lamp, it sticks at dimmest stage 1.
To compound my confusion and found out by accident, if I connect the touch sensor as normal, then lean on (touch) another double insulated lamp with a metal base, the problem lamp operates perfectly through all 3 dimmer stages and off.!!!
I have a pair of these lamps to repair and they both have the same problem.