Update - 18/12/2015
I returned my Humax HDR-1100S to the seller. He said he'd done a HDD clean up, and a reformat, and that it was now waking up from standby as it should. He also said that a factory reset on it's own would not have sorted the standby issue.
However, I was not confident that the problem would not come back and asked for a refund, rather than having the box returned to me. The seller gave me a full refund.
I have now purchased another HDR-1100S and it worked, as it should, straight from the box.
Hope the other members, who had the same problem as myself, have managed to get the issue sorted.