If I had £1 for every time I heard someone make a case for why the UK should be more like Germany by having multiple hub airports instead of just one, then I think I would be quite wealthy by now.
The attractions of having many different hubs in several different cities is obvious, but unfortunately the logic doesn't stand up to scrutiny. Whilst it might be true that Germany is both Europe's most populous country and its strongest economy, neither of these reasons explain why Germany can support multiple hub operations, but the UK cannot.
The reason why it is relevant to compare the UK with Germany is not so much a question of size, as it is a simple question of distribution. For better or worse, Germany has a very different population structure to either the UK or France.
Ask any British or French person which city is the most important in their country, and you will almost certainly be told that London is the most important city in the UK, and Paris is likewise in France. Given that both cities are the capitals and the centres of finance as well as the largest and most economically important, how could anyone rationally disagree?
Now try asking an American or German which is their most important city, and you might get a multitude of answers -- New York or Frankfurt might be global financial centres, but neither is the capital, whereas Los Angeles is the home of Hollywood and Chicago is a leading centre of commodities trading. Meanwhile, in Germany, Munich and Hamburg both weigh in as major financial and industrial centres behind Frankfurt, whereas the largest concentration of population in Germany is actually in the Rhine-Ruhr region around Düsseldorf and Cologne.
The USA is large enough both in terms of population and area to support a hub operation in almost all of its major cities, whereas Germany can support a major hub in Frankfurt together with a smaller, but still significant, hub in Munich and also in Düsseldorf.
The German capital Berlin has a fractured aviation history given that it had three different airports, and the isolation of West Berlin made it impractical as a hub. Yet, when it finally opens next year, the new Berlin Brandt airport will also be a mini hub for Lufthansa, as well as a significantly expanded hub for Air Berlin.
Each of the aforementioned cities -- Frankfurt, Düsseldorf, Hamburg, Munich and Berlin can claim metropolitan areas around 5,000,000 people, something that the U.K.'s secondary cities outside London, whether Birmingham, Manchester, Glasgow or elsewhere, cannot. Even if you added up the metro populations of the second and third cities of the UK and France, you would still find more people living in Paris or London than all those four cities combined.
Neither can any other British cities claim that they specialise in any one particular economic activity to an extent that this must be served by a hub operation. Of course, numerous UK regional airports outside London can easily support what is usually termed as a base operation for low-cost airlines, but this is not the same thing as an intercontinental and interconnecting hub operation by a network carrier like British Airways or Virgin Atlantic (Virgin's long haul flights from Manchester are primarily point to point services aimed at the leisure market).
The argument for a new regional hub is most commonly heard with respect to Birmingham and Manchester airports, yet British Airways used to have regional hubs at both of these airports, before eventually pulling out after many years of loss-making operations. Somehow, Birmingham airport is expected to become massively attractive to new airlines when it opens its new runway extension, even though the British Airways hub operation which did exist there exclusively served European destinations.
If any other network airline wanted to offer more flights from Birmingham or even to offer an enhanced offering of long haul flights from Manchester, the deregulated market makes them perfectly free to do so. The reality is that those airlines that operate interconnecting flights are almost exclusively interested in operating from Heathrow Airport, and when they cannot get suitable slots, they will take Gatwick as a second choice.
Some people argue that this is a self-fulfilling prophecy -- since there are already so many international flights from Heathrow, any new airlines will do everything they can to join in, as each new spoke in the wheel will automatically be connected to all the other spokes.
This argument may be true, but there is little that can be done to run against such a cycle. Proponents of dispersed development may talk of the need to "rebalance the economy" by encouraging more flights from regional airports, but they forget that regional airports have already done extremely well out of the development of low-cost airlines.
Network airlines will therefore always want to serve London above all else, and this is not just because London is London, but primarily because London is so much bigger than any other city in the UK.