By comparison, last year on a Swiss flight from Heathrow to Zurich, I saw the duty manager hand over a couple of sandwiches, cake, apple and banana (all purchased from Cafe Nero) to the Maître de Cabine as they were short one business class meal.

I can fully understand it's unrealistic to expect an airline to procure an additional identical airline meal from an EU outstation these days (as it's all centrally catered), but by empowering staff (either to inform the customer and offer a voucher to buy at the airport, or buying a sandwich themselves at the airport) it is easy enough to avoid the OP's situation and thousands of other people reading a thread about very poor service on BA.