I seem to have defeated the click (cue howls of frustration for tomorrow morning when it comes back).

Pedals. I swapped the pedals and had a quiet ride in this morning
Now I need to rebuild the pedals. Easy enough to do but I need some nested tube spanners to get to the cone nut and locknut inside the pedal so it's off to the lbs after work (I always check out the proper options before bodgying something).

Richard