You mean the pre-flight dining area, not the lounge.

The whole point of the dinmer is that it is really the onboard meal eaten before boarding to maximize sleep. Consequently availability is cabin dependent and nothing to do with the normal lounge access rules - it's not part of the normal lougne food offering . BA have worked so hard on this concept in recent years that little by little, slowly but surely, they managed to transform the pre-fight dinner from something similar to a really rather good hotel-style hot buffet into a masterly demonstration of everything that is disgusting about airline food.