Why? London and the SE have seen the brain drain from all parts of the UK. They reap the rewards of well educated people who move for work and offer nothing back. We need a realignment of wealth across all regions and countries in the UK.
At the risk of derailing the thread entirely, the reason why there has been a brain drain into London and into other major cities is not because of some nefarious conspiracy - it's because cities are incredibly attractive places to live.
The economic agglomeration effects of the city are what make those high paying jobs possible, as well as the amenities of city living.
It is extremely difficult to make smaller settlements so attractive, especially as many of them have lost their traditional raison d'etre with the closure of coalfields etc or the mass employment agricultural economy (agriculture has become incredibly labour efficient compared to historical norms).
Fixing this without totalitarian controls on population movement would be exceptionally difficult, perhaps all you could do is a saturation public transport system so that the effective economic metropolis covers the entire country, but simply demanding that jobs be moved to random towns and minor cities in the North is not going to achieve anything.
On the topic of Manchester Central, I have often thought about platforms near that facility, but it probably doesn't free you from the mass of flat junctions that are the real pain of the area in railway terms.