I've come across a website putting forward the theory that English is much older in England that the Anglo Saxons. They believe that in prehistoric times English was East and the Pennines and Celtic to the west. They also believe the Anglo-Saxon migration to England was almost non existent (they speak of a few hundred "housecarls"), relying on the work of Oppenheimer. http://www.proto-english.org/sor.html
I'm not qualified to judge the linguistic/historical arguments in favour of this, they seem to boil down to "Roman names of English towns are usually said to have Celtic roots, but here's a alternate Germanic root which HAS to be the correct one, because we said so". They also talk about English place names which weren't written down by the Romans, but that's irrelevant.
We now know about U106 which most people consider to be of majority Anglo-Saxon origin in England. But if English really is older than them, U106 would undoubtably have played a role.
I'd be interested in hearing what you think of this theory, and the evidence put forward to support it. I searched the internet but there doesn't seem to be be a proper critique by knowledgeable people on the subject anywhere, here is as good a place for it as any.