Dialect levelling in Britain

Dialect levelling is the means by which dialect differences decrease. For example, in rural areas of Britain, although English is widely spoken, the pronunciation and grammar have historically varied. During the 20th century, more people moved into towns and cities, standardizing the English language. Dialect levelling can develop via the influence of various types of media.
Background
Dialect levelling is a linguistic phenomenon studied and observed by dialectologists and sociolinguists. There are different researcher opinions on what constitutes a dialect in this context. Chambers and Trudgill (1984) choose to view a dialect as a subdivision of a particular language such as the Parisian dialect of French and the Lancashire dialect of English. They feel that standard English is just as much a dialect as any other form of English and that it is incorrect to suppose that one language is in any way linguistically superior to another.
Sociolinguists...