As I understand it: Britain had Celtic people/language, which was influenced by Romans, then Germans, and then the French/Normans. However, English is most similar to Frisian, am I missing something?
I understand Frisian is Germanic as well, but shouldn't English be closer to the type of German spoken in Saxony?
As /u/fella2 said, /r/linguistics is probably a better place for this question.
In fact it's already been asked there in the past. In particular see the top comment there. There was also this related question.
I'd have a quick look at this article then feel free to re-post this question on /r/linguistics. Do review that Wiki article first tough as it'll help people give better answers.
Also for what it's worth: Modern English is more closely related to Scots and Frisian.
You might try the Q&A thread on /r/linguistics.