The map above show’s England’s North South divide based solely on where 50% of the population live based on the 2021 census using official county border.
The blue areas has 50.25% of the population or 28.3 million people and the red areas have 49.75% of the population or 28.1 million people.
In terms of area the two aren’t actually all that different:
The northern section takes up 55.58% to the southern’s 44.42% (these are relatively approximate though, I could not be bothered to research the areas of each county used, although this could easily be done, just slightly time consuming).
This is likely due to the fact that while London and the South-East is relatively densely populated the South-West isn’t.
For other similar maps have a look at: