Just in case anyone finds this thread and has a similar issue. It is now mended. I couldn't shift one of the nuts on the clutch cable, despite using a variety of penetrating oils. So in the end, just yesterday noticed that the local mechanic, who did my last MOT were working yesterday and I was able to get them to work some magic on the cable and replaced it with the spare I have had in the car for emergencies.
A decent drive today suggests that the problem is mended
