In 1235 Jan 19, William earl de Ferrers was supposedly granted, by Henry III, (In year 19 of his reign) a Royal licence to crenellate Leverepul (Liverpool Castle)

"letters directed to his knights and free men requesting them to make him an aid for the strengthen his castle at Leverpul."

Granted at Reading,

Although this document has been considered by some as a licence to crenellate the current opinion rejects this as a licence to crenellate.

Does not seem like a licence to crenellate to me, although clearly Royal consent to strengthen an existing castle.

Original source is

• Calendar of Patent Rolls (1232-47) p89

(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.)

More details about licences to crenellate can be found here.

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