Hogun, I assume you've searched online for any references. The only place I remember mentioning Germanic peoples in Britain before the Romans left was in this book by Bruce Mitchell. He makes a relatively brief mention of there being people from roughly the Saxony area in Britain, possibly as workers in the mines (which I suppose would put them west, rather than east as you inquired). Anyway, there must have been some Germanics there to tell their friends and family back home about the land. There was apparently a sense among the tribes that ended up filling the Roman power vaccuum, that the indiginous Celtic tribes had this great fertile land and weren't really in a great position to defend it. Sorry my memory isn't that great. I don't own the book, and I read it a couple of years ago.

Btw, I highly recommend the Mitchell book (that or any others by him) as an easy but thorough introduction to all sorts of aspects of Anglo-Saxon life, culture, language, literature, etc. Anyone interested enough to join this group is sure to find the book well worth the price.