Question Author
The answer, guys.
1. Take off panel and see the box containing the cable end. Unscrew one small screw to take lid off box.
2. The cable which runs to the waste pipe is attached to an L shaped plastic moulding the long end of which fits onto a brass rod which runs through the bath to the back of the turning disc.
3. The disc can be detached from the other end of this rod by undoing a grub screw which can be accessed through a small hole in the disc.
4. The plastic moulding had split so that the rod rotated in the moulding and did not turn the short leg of the moulding.
5. Araldite the rod into the long leg of the moulding , refit and test.
6. Replacement part would be better but plumbers merchants suggest replacement unit...of course they would.
7. Lucky number ?