I think that a contrite note to Customer Relations is probably going to be your best bet.

There are two other areas to consider, but that will be long after you have exhausted the CR route. Firstly there is the Consumer Rights Act, which seems to have very little collective knowledge in the airline sector (I know a bit more about how train companies run for the hills if challenged on this one, to mix a couple of metaphors). So among the arguments you have there are that the contractural relationship is unbalanced - BA can run the service or decide not to run the service. If a flight crew "forgot" to turn up to work then BA would just cancel the service, rebook everyone and try to wriggle out of compensation too. It's difficult to describe this as a consumer friendly policy. The second and related area is that even if it's ok just to snatch the fare for the no-show, then it is not OK to take the return fare as well - that's still viable and you can't fine customers for non usage. There are a few cases where other airlines - even Iberia - has had to refund that side of the ticket when taken to county court, though that isn't setting a precedent necessarily. Of the two arguments I suspect that is the stronger, but if it is a substantial amount of money then as a very last resort you could get some advice / research on the subject, since I Am Not A Lawyer.