Cheers I wondered whether it was weather proof. I am now thinking along the lines of some sort of masonry anchor. I can see how kinking the bar could get a firm grip in the timber but not so sure how this would work in preset concrete and I want to get on with the patio and forget boxing it out and all that. It's the most difficult patio I've done so far as it is.
I'll stick some images up at the end for constructive feedback!