when Heathrow is obscured by fog, what would your alternate be should you not be able to land at LHR? Would it be LGW?
Probably not, for a couple of reasons. If the LHR weather is foggy or is forecast to be so then LGW will probably be similar. Also LGW runs at pretty much at full capacity and would struggle to handle extra flights. For that reason if the forecast is bad for LHR then BA would be looking at the likes of Bournemouth (previously mentioned)/Stansted/Luton as realistic shorthaul alternates....provided their weather forecast was good enough.