The Gatehouse website record of a licence to crenellate for Biggin Abbey Bishops Palace granted on 1276 May 8

Original source is;

Lyte, H.C. Maxwell (ed), 1901, Calendar of Patent Rolls (1272-81) p. 140 online copy

(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 sources are;

Wareham, Andrew (ed), 2002, VCH Cambridge and the Isle of Ely Vol. 10 p. 123-4
Thompson, M.W., 1998, Medieval bishops' houses in England and Wales (Aldershot: Ashgate Publishing) p. 167
Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol. 3 part 2 p. 403 online copy

Balsham, Hugh of (d. 1286), bishop of Ely

Balsham, Hugh of (d. 1286), bishop of Ely... Nothing is known of his background, except that during the controversy aroused by his election as bishop it was alleged that he was of servile origins... During the barons' wars his diocese suffered severely, especially after 1265, when the Isle of Ely was occupied by die-hard rebels; in September 1266 he was granted the money he owed for military service ‘in aid of the recovery of the Isle of Ely and the pursuit and arrest of the king's enemies who hold out there and destroy the country’ (CPR, 1258–66, 675). Five years later Balsham's own losses were described as ‘innumerable’. Even so, he was more than once suspected of a lukewarm attitude to the king's cause. In April 1264 it was ordered that his barony be confiscated because of his failure to send the knights he owed to the army mustered to oppose Llewelyn. In the following year he was summoned to Montfort's parliament, and probably attended, since he was subsequently prosecuted in king's bench for ‘offences against the peace and other transgressions against the king’ (Jacob, 293). He was only occasionally engaged in public affairs thereafter: in 1274 he was ordered to take steps for the defence of Ely, after rumours circulated of an impending attempt by unnamed enemies to occupy it, and he was present in parliament in November 1276 when the king and his councillors resolved to attack Llewelyn. In May of the latter year he was licensed to crenellate his manor of Fen Ditton, suggesting that he enjoyed easier relations with Edward I than with Henry III. (Owen)

Biographical source include;

Dorothy M. Owen, 2004, ‘Balsham, Hugh of (d. 1286)’ Oxford Dictionary of National Biography (Oxford University Press) online copy (subscription may be needed)