Use the Concorde Room at T5 if you upgrade to F on LHR-HKG. Also starts the holiday on a great note.

All HKG-LHR to London are night flights close to midnight so people bed down faster even thought it is such a long flight, there is more than enought time to eat, sleep and eat again. If others bed down around you, the probability of getting your choice of meal is that much better.

If you take the earlier flight from LHR to HKG, your body clock will be more receptive to two dinners; a lighter snack at the Concorde Room for tea followed by dinner on board.

You do get service breakfast on both flights prior to arrival so that would suit the earlier flight as well.