It seems to me that at least 75% of BA flights I find myself on are "very busy" or "completely full" judging by the cabin announcements, pre-flight sms messages etc. I do take "completely full" with a pinch of salt as occasionally I have been in Y with the middle seat free after hearing that the flight is completely full, but pretty much every flight I get appears to be chocca. The last time I got on an "empty" plane was around 8 years ago flying on Sunday evening of a Bank Holiday weekend from Aberdeen to LHR.