HS2 was shot in the foot as far as air passengers were concerned when the rail industry (acting in its own self interest only) decided it was too costly and it would lengthen journey times too much to include a station at Heathrow. Few air passengers are going to heft themselves and their bags to/from Old Oak while domestic flights exist. There was a golden opportunity: offer through ticketing, protection on later trains / flights should connections be missed, etc. That was all passed up. And now the only way the remaining domestic flights at Heathrow will go away is if its mandated by government.
Those domestic flights are a positive anyway, as they feed UK-originating long haul flights and make them more viable in competition with traffic transferring at Paris, Amsterdam, Frankfurt, Munich, Dubai etc. Its just sad that there are far fewer now than there were in the past. A good number of routes were lost as a result of scarcity in the 1980s, 1990s and 2000s, which made bigger, higher-yielding international routes more financially attractive. The contention that short-haul feed does not support long-haul route development is ridiculous. The wide connecting network (domestic and European short-haul) is an important component of long-haul route viability - its about building critical mass and being able to launch routes that aren’t available from other European hubs, as well as competing with direct point-to-point and other connecting services at those hubs (hence why the EU add-ons are often cheap - to compete). Heathrow needs the short-haul to make some of the long-haul viable, routes that couldn’t be supported by the UK market alone. Its also about serving thin O and Ds over London where the alternative on the continent might be use another mode of transport (e.g. long distance train, motorways) to a major EU airport.
Someone also mentioned Liverpool. Firstly Jet2, Ryanair etc do not have hubs there - they offer services from / to there. To have a hub, you need connectivity between flights and through ticketing, which neither carrier offers. Liverpool is in totally the wrong place for a much up-scaled origin/departure airport because half of its feasible catchment area is unsuitable for residential or business use - its in the Irish Sea (as are big parts of Teesside, Newcastle, etc catchment areas).
People need to get off the question about whether additional pieces of airport expansion make financial sense or not (in isolation). More routes, more connectivity, more choice will always be good for the country and the economy - some major, some minor. The governmental interference / decision should be primarily based on issues such as environment, quality of life for those living near by, etc. Whether it’s financially worthwhile to spend the money to build another runway at a specific airport is an issue for the owners, which make decisions in consort with the airlines that already operate through and those that would serve if more slots were available.
Ryanair (and Wizzair etc.) have demonstrated that the "point to point" model is the most efficient and cost-effective way of providing air services.
No they haven’t. The opposite applies equally: Emirates (and Qatar, etc.) have demonstrated that the most efficient and cost-effective way of providing air services is by using the hub-and-spoke model. Point to point only works in markets that are big enough to support direct services at an adequate frequency - for everything else hubs are needed (whether they are air-to-air hubs or surface/air hubs).