Thursday is indeed a slow day at the office for many. Thank you all for your help. Just to triple-check, I this very minute got off the telephone with BA reservations and sales.

I have no miles. I have no credit, either in the form of refund to my credit card or in the form of a credit against another BA flight in the future. I do, though, have an empty wallet.

In short, BA makes money, and I have nothing at all to show for it, except for a ticket I cannot use.

I do think, though, that a ticket of this type should also have the label 'non-exchangeable' in addition to those of non-refundable and non-changeable.

Thank you, bagold, for the clarification on the tier multiplier. Yes, 1.25 and not 1.5. But in terms of accruing tier points, you do indeed earn tier points for full-fare World Traveller. World Traveller on a restricted cheaper tariff would not, necessarily, earn any tier points, but the journey would, if you are Silver or Go(l)d, still qualify for the tier-bonus multiplier.

Again, thanks to all for your help.