In 1258 Nov 4, Johannes Maunsell, Thesaurarius Ebor (John Mansell; Mannsell) was granted, by Henry III, (In year 43 of his reign) a Royal licence to crenellate Seggewik (Sedgwick Castle)

"... that he may enclose and fortify his house [domum suam] of Seggewick in the county of Sussex, with fosses and a wall of stone and lime, and crenellate and fortify it, as may seem to him and his most expedient, without contradiction or impediment from us or our heirs..."

Granted at Westminster, by the earls of Leicester and Gloucester and others of
the council..

Licence to crenellate granted in 1258 and 1262. Parker did not associate this licence with Sedgwick Castle.

Original source is

• Calendar of Patent Rolls (1258-66) p1

(In fact, the original source given is usually a transcription/translation of what are precious medieval documents not readily availably. It should be noted that these transcription/translations often date to the nineteenth or early twentieth centuries and that unwitting bias of transcribers may affect the translation. Care should also be taken to avoid giving modern meaning to the medieval use of certain stock words and terms.)

Significant later source are;

• Woodburn, Bill and Guy, Neil, 2005-6, 'Sedgewick Castle' Castle Studies Group Journal Vol 19 p75
  Coulson, C., 1994, 'Freedom to Crenellate by Licence - An Historiographical Revision' Nottingham Medieval Studies Vol38 p130n135
  King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol2 p478n45
  Blaauw, William Henry, 1861, ' Royal Licenses to Fortify Towns and Houses in Sussex' Sussex Archaeological Collections Vol13 p104-117
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p402

More details about licences to crenellate can be found here.

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