Mud, blood and electricity. John Christopher's The Prince in Waiting Trilogy
It's a very long time since I read John Christopher's Prince in Waiting Trilogy (The Prince in Waiting (1970), Beyond the Burning Lands (1971), The Sword of the Spirits (1972). Set in a balkanized England cut off from Wales by volcanoes and from Scotland by distance, this is a tale of the Principality of Winchester and specifically of Luke, second son of Robert who is elevated to be Prince.
Luke is nominated by the Seers to be Prince-in-Waiting, but over the years the very things that make him useful to their mission to bring back science will undermine Luke: is honour, his stubbornness mean that he can't give way, and when he ends up in an Arthur, Guinevere, Lancelot triangle, he cannot bend and brings down everything around him.
This is a very macho book. Luke is a soldier and he tells the world from a soldier's point of view. It's very effective, but does mean that we never really get to see the development of science, and what we do see is mostly in terms of weaponry. Other uses for technology are mentioned but stay out of sight. What does come over strongly is the idea that one cannot control the social and political consequences of new tech.