The Norf is not inbred at all,probably half the south is more.
We have had massive influxes of Irish and even Scottish plus a few thousand Italians in the Cities like Manchester and Liverpool going way way back to the 1800s.
We have stereotypes to take the piss,the Norf are known as Northern Monkeys as the Sarf thinks we a are a bunch of Neanderthal cavemen and we call the Sarf Southern Fairy’s as we think they are a bunch of pussies.
Norf is spelt this way as it depicts a Northern accent and Sarf is spelt like that because it sounds like a southerner.
That’s our problem we hate our fellow Brits more because of accents culture and history more than we hate the fucking rapist inbred pedo Muslims goat fuckers.