"Considering that the site of the manor of Thomas Fitz William, king's squire, at Malberthorpe, co. Lincoln, where the said Thomas dwells, is on the sea coast, the king, of special grace, has granted the said Thomas licence that he may put a ditch (fossare) to his manor and enclose the same with walls of 'breke,' stone and mortar (muris de breke lapides et c'clicinis) and crenellate and embattle it and make towers and fortresses there and so hold it to him and his heirs."
Granted at Coventry, by King and of the said date etc. {by authority of parliament}.
Thomas Fitzwilliam obtained a licence to crenellate in 1459. Presumably the risk from pirates or french raids was the reason that being by the sea was mentioned.
Original source is
(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;
More details about licences to crenellate can be found here.
Please let me know if you see any errors, can add information or can otherwise help to improve this resource. Contact me