Originally Posted by
Smirnoff
If you are booked with AY (AY flight number on BA metal?), you will need to contact AY to upgrade. You can only use MMB to select a seat and order SPMLs.
Or did you mean, booked with BA on AY metal?
And remember you can only do this if the TA books it in a proper Y fare without discount (so the fare must not be marked 'IT'). Though people have reported exceptions on this I think.