The disintegration of the British that had survived the contact with Latin during the Roman occupation, began in the fifth century.

Isolation of the British speaking populations in Wales, Cornwall and the north of England and Scotland by the Germanic settlement was one of the main causes. A late British was exported by migration from the south west of Britain to Aremorica (which became known as Brittany as a consequence) in the 5th century. No texts of any significance have survived in British.

Little is known of the British language during the early period prior to the Roman occupation .

Direct evidence is limited to a few names written with the Latin alphabet on coins immediately prior to and contemporary with the Roman invasion, and names of places, individuals and tribes found in Latin and Greek texts. These are often preserved in an abbreviated or manifestly corrupt form. Many of the elements found in these names are readily identifiable and have corresponding forms in Welsh.

There seem to be few British place-names surviving in the area which is known to have been intensively occupied by the English at an early date.

There are more survivors in the West than in the East. Some enclaves of British speech may have existed long after the period of the Germanic invasions.

The British enclave in south Yorkshire called Elmet lost its independence in the seventh century. Another enclave may have existed around Bedford until the sixth century. British speech habits and perhaps native speakers, are indicated in Somerset as late as the eighth century.