In July there was a sale with a fare for the trip I’d booked a month earlier now considerably cheaper. I went to cancel my original booking (accepting the £300 cancellation fee) and buy the sale fare only to find the cancellation fee was around £3k.
What BA have now agreed to do is to refund the original fare minus the cancellation fee but then deduct the sale fare offered in July and leave my ticket intact. Essentially I am now in the same position as I would have been if the fare conditions applied in July had been as advertised.