Some of it may have been down to me not using the correct procedure to torque up the clutch nut - did it the same way on my ETZ and never had any problems.

The clutch hub may have had some damage prior to me assembling it TBH I did not check.

Upshot is that the clutch taper is beyond salvation, so a new one has been ordered, I did run some very fine emery over the taper on the crank and it now looks in pretty good shape - just a few very fine ridges on it.

On assembly I shall be using the technique that Nigel suggested in his response above.