STN-YHM route with September dates are part of the Summer 2007 schedule, which has been on sale since March(?). All long-hauls to YHM have loads exceeding 90%, so the fares you are seeing now are the last few seats and are going to be anything but cheap. It's the old adage, you snooze you lose.
Check out the Winter 2007 long-hauls to YHM (currently only Glasgow and Manchester). The fares are coming in around the £200 mark. Just booked myself for YHM-MAN-YHM and it came in at $495 CAN, approx £235.
By the way, yellow flag, guys. There is a risk of this thread heading the same way as its predecessor, judging by the tone of the posts by ggspn and donttellthepax. How about we see more of that world-renowned British civility?