Here's a relevant map men video about this very matter.

https://youtu.be/ENeCYwms-Cc

Roughly north of a line from the Mersey to the Humber. If we use counties then the southern borders of Cheshire, Lancashire and Yorkshire form the line.

It's essentially this:

I highly recommend Rory Stewart's documentary Border Country: The Story of Britain's Lost Middleland if you can find it anywhere as it does a good job of looking at the North and how it is so strongly connected to Scotland, it's really Hadrian's Wall that divided us along an arbitrary geographical feature because it was easy to defend.

North of the thames

North of the Thames. This means I can claim I moved from South to North.

In actuality the line is somewhere above Nottingham but below Stoke.

For me the North is where you play tig, the South is where you play tag

Abderdeen & Inverness

Once had a Londoner describe the north as "anywhere north of the M25"

I mean, London's a big city but I've never heard any Londoner say this in all my life living there. It's always been "comedians" usually Northern ones as a cheeky insult to Londoners: "Oh look they don't even know geography". Which, to be fair, we probably don't.

Personally I'd say anything North of Sheffield is da Naaarth. Roughly anything above Wales.

Yorkshire and up for me

Anywhere north of me is the north. I’m in North Wales.

Well I live in the absolute middle of the Midlands, so anything north of me is "The North" and anything south of me is "The South".

Simples.

North of Northampton because I don’t believe in the Midlands

Living in the North of Scotland and listening to people referring to anywhere north of Watford Gap as "The North" will always elicit a raised eyebrow from me.

Oh my sweet southern children, what do you know of the true north? Where the sun hides it's face for weeks at a time...

Draw a line from the Bristol Channel to The Wash. That's the line.

I’m a child from a broken home. One parent lived in Yorkshire, the other in the midlands. When they did handover, it was at Donington Park services, the approximate midpoint. Therefore my North begins not far north of Donington Park services.

Chesterfield is one of the points which is 50/50 northern and southern resulting in a real midlands feels.