There is a typescript of a thesis in the NMRC library - Upton, KL, 1978: The Moated Sites of Dorset pp11-12 which suggests an earlier date. The dissertation gives the date of 1248 as the year when Thomas Le Brithun was given the manor, but does not give an exact date for the later official licence to crenellate, except to say that it was during the reign of Edward I. The dissertation allegedly drew upon material then held in the Dorset Record Office (the Dorset file was apparently P6 T.10/1).
Projects Team Officer
Heritage Data Management
National Monuments Record Centre
It should be noted there was a licence granted in 1370 (late C14) by Edward III. Gatehouse
has not seen Upton's Thesis or the referenced Dorset Record Office file. If anyone could make this available Gatehouse
would be most grateful.