If you want to learn anything about the Iron Age and Hill Fort do not read this book. I cannot believe anyone is still writing this tired old rubbish. The authors claims date back thirty or forty years and have long since been shown to be incorrect. There was no invasion, by Celts or anyone else at the start of the Iron Age, which is a century earlier then the authors claim. The first hill forts actually appear around 1100 BCE, 500 years earlier then the authors state, which means they are in fact Bronze Age. About the same time, 1000 BCE the first roundhouses appear, again Bronze Age. These, as the name implies, were round and were still being built after 800 CE. The people on the continent built rectangular longhouses. If they did invade Britain then you have to ask where are the longhouses? After all, you would expect them to carry on building the same style of house. There are no longhouses, is the simple answer.
As for what the people of Britain were called the answer is simple, the Britain's. We know this because that is what the Romans called them. Interestingly, the Romans never mentioned them being Celts.
As for these none existent Celts being driven to the remoter corners by the English invaders, the evidence says otherwise. Some of the earliest Anglo-Saxon houses show British influence in their design. This would suggest that the English and the Britain's were working together. In Wales archaeologists discovered a British round house with and Anglo Saxon house nearby. Again suggesting no one was being driven out. DNA testing is now suggesting that what we are looking at was not an invasion by the Anglo-Saxon English but British people calling themselves English, probably to fit in with the new arrivals.
If these authors actually knew anything about this period they are writing about then they would know that what we are looking at is an invasion of ideas rather then of people. What is more is that the style of design we see in the art of this period is not even Celtic as the real Celtic designs are different. The so called Celtic art seen in the book of Kells is a mixture of Irish and English art. Again we see co-operation rather then confrontation. Claiming that there was a Celtic invasion of Britain is like claiming that just because we have Japanese cars and Japanese cameras and Japanese TV's then we must have been invaded by Japan.
I do not know where the authors got their knowledge of this period from, mine was from studying for a degree in archaeology, but it was completely pointless effort. If I could I would give this book a minus 5 star rating. All I will say is do not waste your money on this book.