Hmm, so I have to apologize. I just assumed that what happened in Britain was similar to other provinces like Gallia or Hispania or the greek east. I never really read much about early history of the british isles so please forgive me. I know there were other provinces which kept more of their own identity than others, egypt is a good example, while others like the gauls or greeks were "romanized" quite quickly although I don't like the term "romanize" here as it was more of a melting of cultures. What the Romans originally provided was actually the basis, the frame, the legal and political background (the Romans were above all practical people and politicians) while the cultural and technical innovations and features were provided by the hellenes, gauls and others. The Romans biggest achievment is being open for such things and providing the possibility for cultural exchange. That's why i don't think the term "romanized" is correct because what the Romans "introduced" in Gallia for example was a hellenized "Romanity" same goes the other way round.

Another thing I would like to add is that "movement" was relatively high in the Roman empire. During the centuries of its existance masses of people moved from one part to another. Just take the army as an example, legionaries and auxilias were moved all over the empire and intermarried with locals frequently and actually often stayed in those areas after retiring. in a timespan of several 100 years this creates quite a mix.