Originally Posted by christep
In general you need to use the lounge in the Terminal from which your flight departs. For OW Emeralds the lounges available in each terminal are as follows (best, in my opinion, in bold):
T2: IB & AY lounges presumably (no personal experience)
AY flies from T1, so you'd typically use the BA Lounge complex and Zone R check-in. If you are AY Silver (ow Ruby) or in C without status, the T1 Servisair lounge can be used.