The T1 F lounge isn't much nicer than the Terraces and when it gets too crowded they stop allowing non-F pax in (T1 is crawling with BA Gold as you might imagine). Probably the agent was trying to communicate this temporary embargo; at other times they do allow Emeralds in just fine (I can confirm based on admitted as QF Plat on a BA CE ticket) ... and the fine print in the OW lounge policy does say "subject to capacity" so they are 100% in compliance even if BA decides "capacity" means 1 Emerald is 1 too many. But trust me, it just isn't worth fighting to get into this lounge. The whole T1 redevelopment is a shambles, along with many of the changes that BA has done in the past year. Making BA the bottom of the top tier in airlines and sinking fast, soon to be 2nd tier if things continue on the same lines as the past 6 months. I fly BA a lot and it has been sad to see all the things that have gone wrong, and stayed wrong. If it goes on much longer I won't be flying BA very much and they'll have one more empty spot in the F lounge at T1.