In Terminal 4, I had assumed that if you can gain entry into a lounge, then you can eat there - if you have a Gold card (or other OW Emerald) and gain access to the F lounge then you can help yourself to anything from the menu. That's because the better food is served in the Concorde room, where only F pax have access.

However, flying out of T4 in F last week, I was asked for a dining invitation by the waitress. I had to go to reception and ask for one, which was gladly given.