In 1143, Roger de Conyers was supposedly granted, by Bishop William de Sancta Barbara, (In year 1 of his reign) a Durham licence to crenellate (Bishopton Castle Hill)

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

Cited as being licenced, but Conyers was chief supporter of Bishop against usurpation by William Comyn in 1143, so more a fortification by necessity than by consent. King notes the document but did not consider it a licence to crenellate. Not, in a meaningful sense, a licence to crenellate although has been called this by some.

Significant later source are;

• Jackson, M.J., 1996, Castles of Durham and Cleveland (Carlise) p76
  King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol1 p140n5

More details about licences to crenellate can be found here.

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