That BA is a plc is doubtless true but what's also true is that places like MAN and BHX and GLA have huge catchments which would keep entire airlines going in other countries - like the one a few deg. West. It's not that BA can't make a buck in the regions, it's that their strategy and corporate structure prevents them from doing so.
It seems inevitable to me that while it will be difficult for governments to restrict LH travel, SH can and will be if *reasonable* alternatives exist so MAN-LHR will start getting pricier.
How about this - BA set up a franchise operation in MAN or use GB and give them the three G-ZZZ* frames which will probably leave the fleet anyway to maintain and operate from there. Give them a free hand with routes subject to aircraft range and bilaterals together with a starter route of MAN-JFK as previously operated by BACX. See what happens.