I would say that generally someone is considered 'low hours' in the UK when they don't have anything bigger than a piston twin on their licence, even if they have 1000hrs TT. I know of people in DHL who had less than 750hrs TT when they got the job (prior to the real low hours recruitment which occured a few months back, but these guys had 757 ratings, so you can see that 'low hours' does not necessarily mean how many (or few) hours you actually have..........!
PP