Guppy
The primary purpose, the reason for being, and the whole reason for being in the cabin by the cabin crew is safety.
You need to get out more.
There you are asking how a poster knew he was in an aircraft at 36,500 ft when everyone knows BA has airshow and now you don't know that BA make an announcement that "The cabin crew are here MAINLY for your safety."
Serving sandwiches and drinks is the fluff...it's something they do when there's time...but it's not the reason they're on board.
Its called providing customer service and it is part of the reason they are on board, if they weren't we pax would travel with another carrier.
Time for you to take another load of rubber dog turds out to HK and leave those of us who spend a lot of time in the cabin who know what we are talking about to reconcile the fact that highly trained and capable crew also serve a customer service function for the majority of the time ALTHOUGH THEY PERFORM MAGNIFICENTLY LIKE THE CREW ON BA038 WHEN NECESSARY