Last post from me I promise!
At risk of committing sacrilege on the BAEC forum, do you have any VS miles (or Amex Reward Points, or Tesco Clubcard points..) lying around?
LHR-HKG on VS PE is by far more cost-effective than an equivalent BA or CX redemption, at 45000 Virgin miles *return*.
You could then proceed from HKG to Tokyo and enjoy a decent 4-5 hour J or F flight for much less Avios than a long haul flight.