You change it to be a not-finance-centered economy.
They didn't build it up on their own. They saw opportunity in western businesses who wanted lower wages and less strict environmental laws, and lured them in. The western businesses then moved all their manufacturing to China who then spied on these factories to out-compete the western businesses with "home grown" products they copied.
There have been an influx of Londoners who have discovered that they can actually afford a house in the North and enroll their kids in decent schools and maintain a good standard of living, especially those who are able to move while maintaining a London salary.
It doesn't fit together as a strategy to me and I don't see it fixing the economy, but I guess they can talk about it as a success?
They will slowly cycle out this historical group of parties resulting in painful economic results and poor social cohesion nationally.