I wonder if anyone else has had this problem using the avios and money redemption option?

We have had to cut short a break in the US due to a problem at home in the UK so have booked two redemption flights with BA from Boston to Edinburgh via heathrow. Only economy was available when we booked them last week but now economy plus has become available. When I called the exec club to change the booking they told me they were unable to do this and would have to make a new booking and cancel the old one. Fair enough, I thought, but there are no more redemption seats available from London to Edinburgh for the second part of our booking, even though we are already booked on this flight.

Having studied the BA website I can not see any mention of this, only restrictions to destinations changes etc. to avios and money bookings. If I had known about this I would have just used avios to pay, which would be upgradable according to the BA website.

Have any other users had this problem and was the operator correct who told me this?

Finally, I am considering asking at the airport if an airport upgrade is available. Does anyone know if this is possible on redemption flights, and if so, if I pay cash for this upgrade would it then earn avios/tier points as a paid for upgrade would (although in my experience they do not seem to credit correctly anyway).