It was formed by adding a 14th-century Bury St Edmunds book to a compendium of material from 12th-century northern England (items 1 to 11 in the Contents).
[1] The latter compendium had once been part of Corpus Christi College Cambridge MS 66.
[2] With its original content, it had at one time been at Sawley Abbey, though it was probably produced somewhere else, perhaps Durham.
[3] It is a source for the Durham poem, which describes the city and its relics.
1.27 as a whole came together in the 15th century or later, but pages 1 to 236 are earlier; and paleographic evidence suggests that, with the exception of a continuation of Gildas' De excidio Britanniae dating to the 14th century, its material shares the same origin.