I think there are a few issues.
As a northerner, I and many around me found it incredibly frustrating that we were pushed into tier 3 without the correct financial support, whilst London had higher rates than us and stayed tier 2. Of course when the decision was taken to move London to tier 3, all of a sudden the financial support was there. It gives the message that the North doesn't matter.
The amount of things reported on the news about London which just aren't reported about anywhere else is probably not apparent unless you're from somewhere else. Things like snow in London, and yet London isn't hearing on the news that it snowed in Carlisle.
Incredibly London centric policies and spend- public transport in most northern cities and towns is fairly crap. Then HS2 comes along to shave off half an hour of the travel time to get to London. Completely disregarding the fact that the issue isn't the intercity travel, its the fact that you'll probably still miss the London train because the local trains are so shit.
And as a northerner who has had to travel to and spend time in London I have never found it particularly friendly. Sure there have been some friendly individuals but the general vibe is very much every man for themselves with little awareness of anything or anyone. It's a stark contrast with my northern town where people are very friendly. I took my dog for a walk yesterday and everybody was wishing happy new year to those they passed etc.
And with regards Grenfell, I can assure you it hasn't been forgotten. But the promise to rectify the buildings retrospectively to remove unsafe cladding in the North seem to have been.