From the beginning of northern summer 2012 (ie last Sunday in March), no more HKG-LHR-HKG and no more BKK-LHR-BKK.
The only QF flights to LHR will be QF1/2 SYD-SIN-LHR and QF9/10 MEL-SIN-LHR.
What you're seeing is the knock-on effects of that decision.