Well after finding some tiny black dots floating on the surface of my clean clutch fluid reservoir, I removed the master cylinder (again), stripped and examined. Wiping my finger around the piston seal (furthest from pedal) I found more tiny black particles. I obviously suspected a faulty seal.
Having read about the problems many others have experienced with aftermarket CMC's I decided to bite the bullet and go HONDA, stupidly expensive. Changing the CMC is a PIA so I removed the drivers seat to gain better access, lay on my back, head in the footwell. Cleaned, fitted, hours spent bleeding the system, I finally had a very nice feel to the pedal. Could be just in my head, but the operation now feels smoother with the clutch operation.
Ive been using the car frequently since, with consistent good operation, no change to the pedal feel and feeling optimistic that the problem is fixed. However, I was quite happy for a while after fitting the replacement aftermarket CMC some time ago, but that ended badly, wait and see how this goes.