I will be BAEC Silver by the time I take a AA flight from GIG to MIA. I'm travelling in what AA calls the main cabin which is like WT on BA. So, no lounge access on that basis but I am reliably informed I can get lounge access as a BAEC Silver and so can my chosen guest if travelling on the same airline.

My doubt is this: Do I use the BA lounge at GIG, as I am a BAEC Silver, or do I use the AA lounge, as I am travelling on AA? I suspect it's the latter but I just wanted to make sure.