Where does it start?
Well my calculation if you divide the UK into simply north and south then the north starts at the northern shore of the river Tees so Middlesbrough is in the south and we can only just about call ourselves northerners.
Therefore how does the BBC class Manchester as being in the north?
Just asking...............

For me, draw a line across from Liverpool to Manchester then to Sheffield and up to Hull and you have the North. The North East could be from Berwick to Whitby or Blyth to Whitby , Blyth to the Tees or Tyne to Tees, take your pick

Liverpool -Sheffield - Skegness is the line..Darlo is the gateway to the North-east..

Starts from the southside of the cleveland hills

North of the Humber

always find places like mansfield a bit strange. hard to class the place as a midlands town really but not quite northern. could be those who live there call themselves northern if they vote labour and the others are midlanders or southerners.

The North starts North of the river Tees and ends South of the Wear.

My highly accurate assessment of where the north starts was done by taking my "Philips Commercial Course Atlas" (1970) and measuring the length of the mainland with a ruler which equated to 9 inches halfing it to 4 1/2 inches which puts it in the River Tees.
Simple and precise.

Thats the one bit of the UK that all Tory governments refuse to invest in.

Typical press quoting corvid19 outbreaks in "North of England" smearing the whole of the area (where ever you think it is).
Do you think they would say "South of England" if it was in the Bristol area? Answer = NO