newyorklondon

Ha! OK, here's the 'honest' version, then. I book a r/t for me and three relatives, with an infant-in-arms ticket (my son) attached to one of the passengers, and reserve all our seats for both legs in advance, gratis. At some point before the flight we decide that our son should actually stay at home with my wife, so it will be just the four adults flying.

We forget to notify BA of this fact in advance, and arrive at the airport and explain the situation to the check-in agent instead.

I presume we would not get charged for our advanced ticket assignments for the outbound leg at this late stage. The infant-in-arms ticket would, I also presume, be removed from the inbound booking at this point. But would that knock out the free advanced seat assignments for the four adults on the inbound?