Obviously, no one on here has suffered the same issue.
It turns out that a simple, if expensive, remedy is just to replace the whole touch pad unit.
Take off the right hand sidepanel by undoing two screws inthe handle carry hole, one screw on hte back face above hte network port.
Un-hook the side panel starting at the bottom and working your way round to the back.
Remove 3 screws and two ribbon cables, two multiway plugs - it is obvious which ones are related to the touch panel.
Pull the whole touch pad module away from the rest of the printer.
Install the replacement by reversing the above steps.
I was lucky in that I had a "spare" MFP375nw printer which had a bent chassis which meant he front door and cartridge rail did not work correctly from which I could source a spare touch pad unit.
Having put it all back together again, I now have a working printer again.
John