Andy- well said.
Shed - I've read the earlier post again and I'm still none the wiser about the public bodies you claim have demonstrated the AC methodology is flawed. Quoting an obscure website & 2 ex-members of the AC isn't solid evidence. I've quoted from mainstream media sources, various industry associations & the evidence based AC report. Even your neighbours in Liverpool favour LHR expansion over connecting through their closest international airport.
I'd also question your assertion that investing £18bn across the regions would generate the same ROI to UK plc. As Andy points out, the only published business cases relate to LHR & LGW so please provide reputable sources of the ROI for the schemes you have in mind.