As a (hopefully) intelligent general reader I was interested to get a sense of what kind of culture, economy, society existed here, and how far it had developed, when the Romans first stepped on our shores. I started with Francis Pryor's "Britain BC". If an overview is all you want, stop there. It's very good. Wanting a bit more detail about the evidence (and a bit less speculation) I moved on to Timothy Darvill's "Prehistoric Britain" which is excellent and highly recommended. Barry Cunliffes' "Iron Age Communities in Britain" is a different kind of animal. It is dealing with the last milennium before the Romans came. It is a brilliant scholarly overview of that period, and presents a highly detailed selection of the evidence available at the time of writing (2005) - indeed this is the stated purpose of the book. It is very well written, it's quite wonderful, but it is hard work - so only come here if you're very very keen to know more.