It is currently quite obvious that London is 'the place to be' for most young professionals and most new businesses. There are certainly things happening elsewhere, in Salford Quays or wherever, but the majority is in London. Unless the UK moves to a command economy it would be quite difficult to change this.
Birmingham, Manchester and Leeds city centres will be just around an hour away from central London once HS2 Phases 1 and 2 have completed. The journey will be extremely reliable, running entirely on new purpose-built infrastructure, and there will be plenty of capacity for all sorts of travellers to use it. This makes it much easier than it is today for people and businesses to move outside of London while still benefiting from the economic power and international pull of the city. To use Salford Quays as an example again, it would allow workers at the BBC to be able to do productive things at both Broadcasting House and MediaCityUK in one day while still being able to commute to work and back home at reasonable times. As railways are a rather symmetric affair, it would therefore make it as easy to live in Greater Manchester and go to London to do things as it would be to live in Greater London and go to Manchester, but one of those options is going to be significantly cheaper than the other.
The absolute worst case scenario for HS2 Ltd is that HS2 becomes a glorified commuter railway when it opens. However, this is not as bad a thing as it may originally seem as the effects of this will eventually balance out to produce the same benefits that they are predicting now. If you have a company in London, and the majority of your staff live in Greater Manchester and commute in everyday, it makes sense to look at opening an office in Manchester so that you can pay your staff less by the value of an HS2 season ticket. Let's say the London office pays some staff £50,000 a year, and an HS2 season ticket from Piccadilly or New Lane costs £10,000 a year. You could open an office in Manchester or Leeds, with a far lower office rental cost, and pay staff members there £10,000 less a year without any of those employees losing money. You know that it is more than easy to go between the two offices in the course of your business, as they are merely an hour or so away, and you know that the journey between them is comfortable and conducive to doing business in the meantime with the high speed internet connections every passenger will have access to. You can keep your London office open for the few staff that absolutely have to be in London to do their work and all the people who don't absolutely need to be there can move up north. As the cost of housing in northern cities is significantly lower, and can be kept lower much easier as these cities have space for millions more people to live there without skyscrapers or Crossrails being needed, you can reduce your northern staff wages again without them losing out.
Now, there may be subtle things that mean that it doesn't end out all as rosy as I am picturing it but the question has to be asked whether not building HS2 would make the picture any more rosy. If we don't build HS2, it isn't going to help people move to the north because the value of having connections within an Alpha++ city - London is only matched by New York and is surpassed by no one - is significantly higher than the reduced costs of moving out to another city.
