Let us suppose Northolt was opened to commercial passenger traffic for a few years. Which airline would likely be the primary beneficiary given the current physical constraints such as runway length and no significant expenditure on transport links (ie no people transit or new roads) ? Would the biggest beneficiary be Flybe by any chance, in the hope of pinching some traffic from BA and Aer Lingus ? Could this therefore all be a bit of rather subjective public spin by a company with very specific interests ?
But to be fair to them, maybe it does partly solve a problem. If you can take LON destination domestic traffic out of LHR and route them through NHT there could be the possibility of slots being opened up for longhaul traffic. Connections to central London are there through Ruislip and Hillingdon so although self-serving, it could be an interim move.
Because of the proximity of LHR, the alignment of the rwy, and the presence of GA and the RAF, NHT commercial operations would be very limited, so there is no question of the trunk domestic routes shifting from LHR to NHT.
NHT would be available for thin domestic routes only, perhaps the ones that were formerly at LHR and the kind of routes that might be suitable for a BE-type operation.
Some investment at NHT would be necessary, such as a terminal, railway station(s), etc.. BE appear to believe that there is a business case for this.
Clearly there is no question of NHT being used as LHR’s third rwy, so this gives the impression that (a) BE would like to operate from an airport west of London (for good commercial reasons) and (b) BE would like to operate from LHR when/if conditions ever allow (again, for good commercial reasons).