Why would anyone go via BHX, an airport with far fewer destinations than LHR, whether by HST or not, when one can go via LHR or several other London airports.
Obviously the idea of flying to/from BHX would only ever apply to someone starting/ending their journeys in the centre of London and Controlx mentions that 3 hours would be needed. It would realistically have to be more than 3 hours, unexpected events have to be allowed for.
Anyone travelling from the conurbation can forget it, as it could easily take up to 2 hours just to get to Euston.
Even in the unlikely event of the flight being dirt cheap, this would be more than wiped out by the high train fare.
Think again Justine.