This is a copy of the 1225 Magna Carta and Charter of the Forest run into one. 1 However, at the bottom of the folio with the 1225 Magna Carta’s chapter 37 (on scutage), a clerk has added passages from the end of the 1217 Charter about the passing down of the concessions saving everyone’s existing liberties, destroying the castles built in the civil war, and the witnesses being those named above. It seems probable, therefore, that Cerne had a copy of the 1217 Charter. For a full discussion and images see my Feature of the Month on ‘The Cerne Abbey Magna Carta’.
The cartulary is listed in C. Breay, J. Harrison and D. M. Smith, Medieval cartularies of Great Britain and Ireland (London, 2010), no.218.