Britain c. 802 was divided among competing groups, with most of England controlled by the Germanic Angles, Saxons & Jutes and Scotland divided between the Picts (the kingdom of Fortriu) & the Gaels (the kingdom of Dalriada) from Ireland who together combined to form the basis of the Scottish nation. 'Britons' here means the Celtic peoples -- including the Welsh in Wales & the Cornish in Cornwall (here labeled 'West Wales') -- pushed out of England by the Germanic tribes.
The Danelaw, as recorded in the Anglo-Saxon Chronicle (also known as the Danelagh; Old English: Dena lagu; Danish: Danelagen), is a historical name given to the part of England in which the laws of the "Danes" held sway and dominated those of the Anglo-Saxons. It is contrasted with "West Saxon law" and "Mercian law". The term has been extended by modern historians to be geographical.
Celtic map. Celts or Kelts were an ethno-linguistic group of tribal societies in Iron Age and Medieval Europe who spoke Celtic languages and had a similar culture, although the relationship between the those elements remains controversial. Today, the term Celtic generally refers to the languages and respective cultures of Ireland, Scotland, Wales, Cornwall, the Isle of Man, and Brittany, also known as the Six Celtic Nations. These are the regions where four Celtic languages are still spoken.