Kicked out of F dining room at IAD ...
For reasons too boring to detail here, I ended up at IAD nearly 5 hours before a UA flight to GVA (flying in C). In best FT fashion, I decided to lounge hop, so first I tried out the UA Red Carpet Lounge. After a while, I checked out the LH Senator Lounge (using the UA C boarding pass plus M&M Senator Card). Then I went over to the nearby BA Galleries. Since I have Gold on BA, they kindly let me in and, then, after a moment of confusion, agreed that I could use the First side. I noticed they were serving dinner after about half an hour, so I went over to seat myself. I was provided a menu by the dining room manager, but then one of the lounge staff commented to her (not so quietly or politely, frankly) that I was not a First passenger. The DR Mgr. asked for my boarding pass. I let her know I was there "on sufferance" due to my Gold card, which lets me use the First lounge, but that I was not flying BA that evening. The DR Mgr. called over the Lounge supervisor who let me know that I was not entitled to dinner, but was welcome to use the lounge.
To her credit, the Lounge supervisor was very polite and apologetic (unlike DR Mgr.) and I did my best to reassure her that it was not an issue for me (even if a teensy bit humiliating). I did suggest they might want to let others in my situation know when we checked in at the desk, and that a well placed sign would also not be amiss.
This is really just an FYI post - maybe the rules are clear somewhere, and I confess I am too lazy to hunt around BA.Com. In any event, I will be able to "enjoy" the dining at the CCR in London when flying F to Australia later this month, and, as it turned out, I enjoyed a better-than-expected meal on the UA flight in the end. I had just really thought to try out the BA dining experience and maybe gain an extra hour or so of sleep on the flight. Silly, greedy me!