It may have been an illusion for Boris, but for many towns in the North who remained under Labour control, who are now like 'ghost towns' with shopping malls half empty, no proper high street and no new industry startups in over twenty/thirty years, except such as coffee bars and nail bars, etc. that last a year.... maybe only six months, then shut down. These towns need major new investment. Many towns have been living on scraps, either from so called regeneration projects or some were EU funded, but in many cases, it wasn't local industry that got the contracts or the benefit of actually doing the work.
Here's an example of what I mean, where I live there were two EU special projects 5th and 6th (in 2007-8 and in 2010) on a list put forward by the local council and with support from the local chamber of commerce that were accepted for EU funding. They involved work in a local park building a kid's playground and improving the gardens/access in two old folk's homes. The total value was around 15000 euros, the local Labour council let both contracts to companies from outside the area. So, although local children and elderly folk eventually saw the benefit, local industry didn't.
'Levelling up' is required and Labour needs to do it properly.