Many thanks for all the help....
Again I'm amazed by the speed, helpfulness and depth of knowledge of the FT community.
I'm going to drop BA at CAI an email, and see if they can do the ticket. Reasons: More miles on the BA Amex Card, another 3.5K to my next 2-1 voucher, no currency charges - last time I was charged in GBP, also ability to call BA direct for the changes. I may also score my 1st e-RTW, as BA can (apparently) interline with AA and CX. We'll have to see.
If BA won't play ball, EMECO will certainly be my 1st port of call. I'll post my progress in this thread.
I'm finalising my route, which will include CAI-LHR-SFO xxx ANC xxx JFK-HKG-SIN xxx HKG-LHR CAI. Just need to find a few interesting flights for the xxx's. I'll probably book next week.
Thanks again,
M-P