Thank you Joao & John for your replies.

On our 8 year old trees there was no bark damage at all but there was considerable leaf drop. The lenght of shaking cycle appears critical as far as leaf loss is concerned, there is a point where optimum fruit removal has occured and shaking beyond this point causes heavy leaf fall. This seems more pronounced early morning when dew is still on the leaves.
I had hoped we may have received a post from someone who had several consecutive year experience shaking the same trees to be able to gauge any long term positive or negative effects on tree health. Maybe that post is still to come??

Regards
Michael Pimm