Originally Posted by
Gabo000
But the seats had already been reserved for me by the BA employee, so I don't understand why it shouldn't work now.
On CheckMyTrip you can see the vacant seats that are available. Some are marked with an X, they are not available.
Seat availability depends on a lot of factors such as passenger status, fare code, marketing carrier, etc. What you see as available on checkmytrip may not match what is available for your particular ticket.