During World War II a manuscript book was unexpectedly returned to King's Lynn's archives. This volume had first been recorded among the town's official papers in 1446 but by the nineteenth century, when the first systematic cataloguing of the archives was done and the first transcriptions and translations of their contents were published, it had disappeared. Still unpublished today, William Asshebourne's Book comprises 129 folios of personal records and memoranda compiled by Lynn's town clerk between 1408 and 1417. These years cover a time when the port experienced a period of protracted unrest which has interested many historians, not least because Lynn during those years has been described as the sole example of non-burgesses participating in town governance in the whole of fifteenth-century England. This article will establish the value of William Asshebourne's Book in explaining these apparent idiosyncrasies and show how the Lancastrian usurpation precipitated internal problems within the town's élite, and then exacerbated them as Lynn's wealth and position attracted the attention of opposing factions within the national Lancastrian hierarchy.

Modern-day King's Lynn bears little relationship in size, status or wealth to medieval Lynn. In 1377 its tax-paying inhabitants had numbered 3,217 this figure has been used, variously, to estimate a pre-plague population of between 5,700 and 9,000, falling to perhaps 5,500 post 1349. In the 1334 Lay Subsidy Lynn was taxed as the eleventh richest provincial town, and the Poll Tax of 1377 suggested it was still the seventh most populous. Such bald figures do not testify to the importance of the port which had become significant in regional, national and international trade. Indeed, Lynn was important enough in national terms when Asshebourne was writing his book to warrant the attention of two kings, two princes, the dukes of Bedford and Clarence, Thomas Beaufort duke of Exeter, the archbishop of Canterbury, and four bishops of Norwich in their efforts to effect compromise and peace between its warring factions.

The town had been founded in the last years of the eleventh century by the first bishop of Norwich on the edge of his estate at Gaywood, at the southeast corner of The Wash. By the end of the thirteenth century its hinterland comprised nine populous and productive counties, served through an extensive river system, as far west as Warwickshire and as far south as Bedford. In 1204 the borough had been chartered by the bishop. By then its inhabitants had already become wealthy and influential and just six months later the merchants acquired their own charter from the king, for three palfreys and 100 marks (£66 13s 4d).