ISO well-researched/peer reviewed nonfiction recommendations for pre-Christian religious/spiritual practices across the British Isles and Europe

Most interested in;

• English and Scottish, but interested in it all
• anything that explains the intersection of Scottish and Irish mythology going deeper than a simple "Scottish practices were probably similar but less primary sources exist"
• Symbols across historical religious sites
• Well-researched reconstructionism from a modern pagan perspective
• Books that show how lsurviving pre-Christian traditions and folklore exist in cultures now (deeper than "Easter was stolen off the pagans")

Looking for non-fiction books that are heavy on the references for further reading and that are based off of as much historical fact as possible, I'm not interested in New Age information or anything particularly twisted by modern spiritual thinking and Victorian romanticism. Also totally open to interesting academic papers/journals! Although I'm not doing formal academic research, please suggest things that would be acceptable to reference in research.

Thanks in advance!