As an island, Britain has juggled two conflicting influences on its languages. A constant inflow of global cultures has brought new words and phrases while, but at the same time, until the late 20th century, limited mass travel saw individual regions remaining close-knit.
So early settlers – Romans, Anglo-Saxons, Norsemen, people from the Germanic countries – brought their languages with them, while the Celtic tongues of Wales, Scotland, Ireland and Cornwall stayed discrete.
Scholars also studied Ancient Greek, the legal system conversed (from 1066) in French, and the language of the Church was Latin. The language of ordinary people thus became an ever-evolving dog’s dinner of everything, with regions developing their own blends and words. London’s dialects pretty much changed with every ship that docked.
Also, before modern transport, people were less mobile. Dialects and accents in each area were steeped in their own rich variations – the same, yet different from the rest of the British Isles.