In 1346 Sept 15, Abbas et Conventus de Langeley was granted, by Edward III, (In year 20 of his reign) a Royal licence to crenellate Langeley (Langley Abbey)

"quoddam campanile infra Abbatiam de novo construendum
Licence for the abbot and convent of Langeley to build a belfry within the abbey and crenellate the same."

Granted at Westminster, by privy seal.

Parker identifies this as Abbot's Langley, Hertfordshire. However there was no Abbey there (It was a manor of the Abbot of St Albans). The VCH records the licence for Langley Abbey, Norfolk. The crenellated belfry can hardly have been defensive.

Original source is

• Calendar of Patent Rolls (1345-48) p164

(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;

• Coulson, C., 1982, 'Hierarchism in Conventual Crenellation' Medieval Archaeology Vol26 p94
  Page, Wm (ed), 1906, 'Houses of Premonstratensian canons: The abbey of Langley', VCH Norfolk Vol2 p418-2
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p414

More details about licences to crenellate can be found here.

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