thanks for the suggestions.
yes, I did replace the fan clutch, and yes my mechanic did the tea towel in the blades test beforehand to check it was bad
Checked yesterday and found the engine temp sensor is kicking the fan in at high speed when the temp gets to 107 or thereabouts, so not worrying about that any more.
Having checked all the components, seems the fan control is acting as it should, which leaves only the cooling process.
A failing fan I find unlikely seeing as it actually runs. Can't think why an electric fan would slow down instead of stop if it was failing.
The other suspect is the AC condensor, core or whatever its called that sits in front of the radiator. its either running too hot or its not letting air through at all, which seems more likely. Plan to try cleaning it out this weekend.