I would suggested BA F to PKX, then get a cash ticket from Beijing to TPE (as routing via HKG is such a detour), then use Avios from TPE to HKG on CX and BA F to LHR.
The reason I suggested going with BA is that the CX flight from MAN to HKG lands really early in the morning and it would make it a very long day before bedtime. Also, CX business or BA First, I would say BA F is slightly better. And reason for outbound to PKX, so that you can enjoy the lounges at HKG before the flight back to LHR.
Have fun!!