In 1343 Nov 20, Johannes Heroun [Heronn] (Sir John Heron) was granted, by Edward III, (In year 17 of his reign) a Royal licence to crenellate Crawelawe (Crawley Tower)

"mansum suum de Crawelawe"

Granted at Westminster, by privy seal.

I've not investigated the tenurial history of Crawley but, as a younger son, there is a possibility of some question as to John's holding.

Original source is

• Calendar of Patent Rolls (1343-45) p143

(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. Licentia is best translated as 'freedom to' not 'permission'.)

Significant later source are;

• Emery, Anthony, 1996, Greater Medieval Houses Vol1 (Cambridge) p159
  King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol2 p367n99
  Bates, C.J., 1891, Border Holds of Northumberland (London and Newcastle: Andrew Reid) p9
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p413

Sir John Heron

The Heron's were a prominent Northumberland knightly family. A John Heronn sat in parliament in 1357-8 as a representative for Wallingford.
Sir John Heron of Eppleton or Crawley ancestor of Herons of Eshot, younger brother of William Heron (granted licence to crenellate Ford 1338). His son was Sir William Heron of Applynden, Lord Say.

More details about licences to crenellate can be found here.

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