I am flying the following itinerary with no status soon. I will however be platinum upon return thanks to the Plat Challenge and FT!

DFW to LGW on AA
LOOOOONG layover
LGW to DUB on BA

My question is, if I do get upgraded to Biz class on outbound AA flt, what, if any, lounge will I be able to loiter in at LGW? And what could I expect?

Also, do I clear customs, etc in LGW and have to re-clear security, or do I stay airside and clear customs in DUB.

Thanks to all in advance.