I'd actually be happy with afternoon tea if the sandwiches were of decent quality and they served a champagne which was remotely drinkable.

What you must do when travelling on an afternoon tea service is to request a special meal (seafood is my choice) if you book more than 24 hours before departure. You do this through manage my booking.

If less than 24 hours before departure and you've not reserved a special meal it's always worth asking if they have anything more substantial in economy. I know on the band 3 flights (e.g. PRG) the flatbread offered in economy is nicer than those sandwiches in CE.

Ordering a special meal gives feedback directly to BA where it matters, plus you get something nicer to eat. If more people order special meals they'll start to realise it'd be more cost effective just to offer decent food to begin with.

Also send a message to customer relations about your experience.