So he didn't pay, payment was on hold, OCUK did not see money until fraud check cleared. All deals are subjected to availability, and when he paid it was no longer avaiable, they recived physicial money from someone else who purchased product on website with discount.
They accepted an offer he negotiated and were waiting on payment to clear.
While the OP might have no legal recourse in the matter, I'd argue that OCUK should have held the item for him under the circumstances as it would have been the decent thing to do.