So I'm curious about what was going on after the Romans left. Was this Christian community directly descended from the Christianity that existed while the Romans ruled? Or was it the Irish/Celtic kind that only came back into Northumbria a century later, after the Angles had swept through and paganised the land for a while?
Are the two distinct in archaeology?
A good book which includes this topic is "Britain and the End of The Roman Empire". The Author is Ken Dark and it is published by Tempus in both England and the US. The paperback is $29.99 and is up to date as it is possible to get without going to primaty sources. I have just been re-reading my copy as part of a course I am taking at Liverpool University.
PS I like the site. Well done for getting it up and running