In which case that solves the mystery, and indeed from a Blue perspective this is how I believe Basic fares should work. The underlying logic of the change they made to seat selection was to row back on the ire that BA got when their frequent flyers - who don't always book their own tickets - found themselves losing what was seen as a core perk of BAEC, namely BA's seating logic. So for Bronze/Ruby and above there should be no difference between Basic and Plus fares for seating. For Blue / no status then the seat allocation is given by the system and any changes come at a price. After check-in has been completed, 45 minutes before departure, you can ask a gate agent to move you to another position gratis. Plus careful use of self service check-in machines may still allow it.