Currently Dragonair (KA a partner of CX) has a nonstop flight REP-HKG many days a week. Then you can easily connect to one of the 5 daily CX flights. However, availability on REP-HKG might be limited.
MH has a nonstop REP-KUL connecting in KUL to LHR. Connecting times might be less good as only two MH flights.
You might be better off buying the short segment. HKG-LHR in J is only 60K one-way in J while KUL-LHR is 70K, CURRENTLY.