The English language is constantly evolving, with slightly different ways of pronouncing words gradually developing.
With modern media, many of those change now affect the whole of the country (or the whole of the English-speaking world) almost simultaneously but, prior to the coming of the railways (which, in historical terms, was only a short while ago) most people never ventured more than 5 miles from their place of birth, throughout the whole of their lifetime.
So each geographical area would undergo it's own evolutionary changes to the spoken language, which would be different to those in other areas. Hence there was no reason why spoken English in Newcastle should sound at all similar to the same language when spoken in York or London.
Chris