Correct form of Iron Age British names

[cagwinn]

Does anyone know what the most likely correct form of famous ancient British names would have been. We know the Latin renderings but is there any concensus on how the Britons themselves pronounced these names?

For example you see Caractacus rendered as Caratacos, Caradoc and Cassivellaunus as Cadwallon - I know the latter two examples for each are taken from Welsh traditions, but as I understand it these came much later, and the western Brittonic language could have been quite different to the eastern.

Brittonic gradually gave way to Welsh, Cornish, Breton and Cumbric by the 6th century AD - it was a slow process, of course, and each language developed its own unique traits, but generally speaking Cumbric and Welsh were closer to one another than they were to Cornish and Breton, which make up what is called the South-West branch of Brittonic...it is likely, though, that all remained mutually intelligible well into the medieval period.

The proper Brittonic form of Caradoc was Carata:cos (a: = "long a"; the names means "Loving, by the way; and is cognate with the Modern Irish name [Mac]Carthy). The spelling Caractacus, which non-etymological, comes to us from a later manuscript corruption that arose during the middle ages or early modern period, IIRC.

Brittonic Cassiuellaunos (Latinized as Cassiuellaunus or Cassibellaunus in some later manuscripts) became Welsh Caswallon; Catuuellaunos (Latinized as Catuellaunus) gave us Welsh Cadwallon.