A book which helped changed the course of English history, part of the evidence Henry VIII and his lawyers gathered in the 1530s to help win an annulment from Catherine of Aragon and ultimately to break with Rome, has turned up on the shelves of the magnificent library at Lanhydrock, a National Trust mansion in Cornwall.

The book, a summary of the theories of the medieval philosopher and theologian William of Ockham, has been newly identified by a US scholar and expert on the history of Henry’s library. The book was damaged but escaped destruction in a disastrous fire at the house in 1881, and crucially the fly-leaf survived. It still carries the number 282, written in black ink in the top right-hand corner, which Prof James Carley identified as corresponding with an inventory taken in 1542 of the most important of Henry’s books, five years before the king’s death.

Paul Holden, the house and collections manager at Lanhydrock, said: “It was an amazing moment. The old long gallery here is about the length of a football pitch, and the professor lapped it about six times when we found the book.”