Thanks for all the suggestions, I did spend time with him in the rescue centre and stroked him,/handled him, he seemed fine and very friendly. He's affectionate still, just the odd swipe, though Im learning his body language a little and withdraw my hand when he seems to be about to react.
The clawing only really started when I got him home, although he is actually a lot better this morning. Seems much much calmer.
Liz, your comment about him finding the open space frightenning was something that never occured to me, I just assumed he would be glad to get out of the small pen but, thinking about it, it must be so overwhelming for him. He has started to explore today tho, sniffing around and has jumped on the windowsills so he can look outside.
I will try the Feliway/felifriend if he's still jumpy but I suppose time and patience and learning to trust me are what he needs.
Think it's also Im a bit wary of him, had previous cat 20 years and knew all her little foibles, it's a bit odd having a "strange" cat.
Im sure we will get used to each other, he really is a sweet cat.