Thank you for the replies.
I am not travelling in WT+ as I'm not too fussed about the extras it offers, plus the price difference was not really justifiable to me, the fact the cabin is mostly over the wing doesn't really sound appealing to me anyway as I very much enjoy the view on TransAt flights.
Groundhog, the seat plan for all 4 of my flights (EDI-LHR-ORD//TPA-LGW-EDI) is available for viewing without payment being taken, so perhaps the system has changed now! I certainly hope you get somewhere with BA customer service.