Surprise upgrade
 

I was travelling NRT-HKG-LHR-CPH last saturday on CX. Much to my surprise the HKG-JHR segment was upgraded from J to F.
I have no status with CX but do hold a Gold (emerald) card with BA.
Is it normal for CX to upgrade partner airline passengers?

Yes, I believe it's been reported that after its own top-level elites (Marco Polo Diamond I believe), CX will do op-ups for other OneWorld Emeralds, before taking care of its own lower level elites. Apparently this is in contrast to Qantas.

But keep in mind they only do these upgrades when they have to - i.e., when a class is oversold and they need to bump people up, rather than bump people off.

Sadly, J was not full (nor was Y) on my recent HKG-LAX flight, and even though I believe there were only 2 pax in F, they did not do any operational upgrades.

Op up... always luck of the draw...

I've received the same op-up long haul from J to F on CX. A true surprise and total delight.