Originally Posted by
DeathSlam
I would assume so.
Should be able to use the lounge as well.
The principle being that the 'long' journey is in J.
(This assumes that both flights are with BA on a single ticket)
Lounge is not dependent on the flights being on a single ticket. Separate tickets are fine, but baggage allowance, security etc. will not work "spill over" on separate tickets.
Not sure if benefits as fast track works on one ticket either, but lounge definitely works regardless. They may reject you at first at the entrance, but the OW rules are quite clear on this so just point to those.