Just a drive by to say many thanks to nux and the other people here who answered my question. Availability suddenly opened up on my preferred travel dates to Tokyo so I got 2 Avios upgrade fares from PE to CW for £2600 (which is currently less than the cost of one cash only CW fare). My travelling companion and I are chuffed little penguins and it only happened because I took the advice of you guys and was checking availability every day like an obsessed fiend.
Even better, I'm putting my hotel loyalty card points to good use to reduce the cost of the hotel stays.
So basically, my credit cards and bank manager are really grateful to you.
1F