The classic study remains that by J. C. Holt, Magna Carta, first published in 1964, now in its second edition (1992). Holt’s The Northerners (1961, second edition 1992) is indispensable for the history of John’s reign, and offers a very good read.
Amongst the small library of books dedicated to the subject, I have made particular use of Faith Thompson, Magna Carta: Its Role in the Making of the English Constitution (1948), and Anne Pallister’s sparkling Magna Carta: The Heritage of Liberty (1971).
For background histories of Angevin England, David Carpenter’s The Struggle for Mastery: Britain, 1066–1284 (2003), and Nicholas Vincent, A Brief History of Britain: The Making of the Nation 1066–1485 (2011) offer a framework. The classic study remains (the crabbed, bizarre, but still compelling) J. E. A. Jolliffe, Angevin Kingship (1955), written by an Oxford academic in almost total isolation from other modern approaches, yet informed by a deep understanding of the charisma of tyrants acquired both at Keble College Oxford and during Jolliffe’s war service in Brazil.
The best of the modern biographies of King John is that by W. L. Warren, King John (1961), with a significant collection of essays edited by Stephen Church, King John: New Interpretations (1999).
The history of medieval law has tended to develop as an arcane science, closed to enquiries from hoi polloi. There are nonetheless introductions that will lead readers as far as the temple gates, by John Hudson in his two books, Land, Law and Lordship in Anglo-Norman England (1994) and The Formation of the English Common Law (1996), and by Bruce O’Brien, God’s Peace and King’s Peace: The Laws of Edward the Confessor (1999). For a particularly revealing history of the meaning of ‘liberty’ to those living both before and after the Norman Conquest, see Julia Crick, ‘“Pristina Libertas”: Liberty and the Anglo-Saxons Revisited’, Transactions of the Royal Historical Society, 6th ser. 14 (2004): 47–71. There is much that is essential expounded in essays by John Maddicott, ‘Magna Carta and the Local Community 1215–1259’, Past and Present, 102 (1984): 25–65; David Carpenter, in various of the essays in his The Reign of Henry III (1996); and by Paul Brand in his collection The Making of the Common Law (1992). The adventurous are recommended to return to the grandfather of modern legal history, Frederick William Maitland, whose History of English Law (2 vols, 1895; several modern reprints) is not only as learned but a great deal better written than much that has followed it.
The material above relating to the reissues and documentary history of Magna Carta is derived from the survey I carried out in 2007 for the sale of Magna Carta in New York, published, with lavish photographic reproductions, as The Magna Carta (Sotheby’s Sale Catalogue, New York, 18 December 2007). One bizarre subhistory here is told in greater detail in my booklet Australia’s Magna Carta, published by the Australian Senate (2010).