Originally Posted by
Globaliser
If you find that the last sector of your ex-EU has been cancelled, you can accept the cancellation and you will get a refund from BA which may be for a pleasantly surprising amount. So that's not an issue.
But that's not the situation you mentioned before: the passenger has bought a non-refundable fare and the airline is ready and wiling to carry the passenger to their ticketed destination, but the passenger wants to change something. The non-refundability of the ticket does not bar the airline from charging for the change. It happens all the time.
Perhaps we can express the issue in an airline agnostic way:
Two parties have entered contract for a service. The purchaser had the option of two services, one of which was higher priced - the purchaser opted for the lower priced service.
The vendor stands ready to render the service to the purchaser, but the purchaser is choosing to avail themselves of the higher priced service without recourse. The vendor is claiming the right to charge the higher price for the service actually provided.
The fact that the lower priced service entirely contains the higher priced service - and is thus something that the purchaser can unilaterally avail themselves of - is somewhat peculiar to the airline business [hence the plethora of analogies], but is not relevant.