Flexible ticket
When you make your booking on ba.com you can choose between 'Lowest price' and 'Flexible' ticket type.
If you have already made your booking and you are not sure if you have booked a flexible ticket, you can go to Manage My Booking and check your selling class.
The following selling classes mean that you have booked a flexible ticket and that you are entitled to book your seat in advance free of charge: F, A, J, C, W, Y for all flights, plus D for European flights.