I find CX's prices on the HKG-LHR route aren't usually competitive (unless you fly to Taipei first and buy a return TPE-HKG-LHR) as like most airlines, CX charge more for flights departing from their home airport. You can usually get a much better deal in J with Emirates often saving HK$10-20k+ compared to the equivalent CX price. Plus you get the Emirates limo service at each end. It more than compensates for the stopover in Dubai.