Went BA F to Denver last month.

Not a single item of gluten-free food on the LHR T3 First lounge menu. Staff just plain rude in restaurant when asked about things like soup.

So we left the lounge and went upstairs to the one that takes Priority Pass. Super-friendly staff, nice views and some gluten-free options.

On the aircraft, there were things that could be done to make most options gluten-free - although, especially on a flight to the States where the article above claims that 33% are trying to be gluten-free - one would have thought they could use cornflour to thicken sauces instead of wheat.

On the way back, the food in F was so crap it wouldn't have mattered if it was gluten free. A BA cabin crew who came to us the other day said poor quality food was an issue ex-USA.

So maybe do as we did, and dine before. Then the onboard food is just a snack to have with the LPGS!