I did this using AM for HKG-LHR-HKG in February 2010, kept on checking every day for a few weeks and finally got availability both ways 3 days before I was due to depart. Has to be done on a return, as they don't offer one way upgrade.

Also it has to be done at least 48 hours before departure, and it MUST be done by CX. Also you need to cancel the underlying booking immediately after ticketing the upgrade or both may get cancelled by BA's IT. So basically you need to get your TA to talk to CX directly, as CX cannot touch any BA bookings.

Also, once you achieve the impossible and get it ticketed, be prepared to have to fight with MPC to get your miles posted to MPC. The upgrade tickets into U class on BA and this shows up as fully free ticket and only and miles don't post and only after writing letters and lots of phone calls will you get your miles.

Although it's good value miles wise, it's frankly not worth the headache it causes both pre- and post-flight.

See this thread for more info: http://www.flyertalk.com/forum/catha...ting-time.html