Not currently available for QR8 (or any from LHR on 18 Feb) I'm afraid. You can ask at airport but they do limit airport upgrades (with qmiles) to 2 J seats per flight from LHR.
If it helps, LGW is currently showing 1 J award on QR330 and 2 J awards on QR328.
You should be able to check on QR website (toggle to "use qmiles" when searching for your flights) and/or try a BAEC account. For your future reference
