HEFCE, the precursor to Research England, announced in 2016 (http: //www. hefce. ac. uk/media/HEFCE, 2014/Content/Pubs/2016/201636/HEFCE2016₃6. pdf) that "we intend to move towards an open-access requirement for monographs in the exercise that follows the next REF (expected in the mid-2020s). " This was published in 2016 as, "given the length of time required to produce and publish monographs, " HEFCE wished "to give due notice to the sector" by
Martin Paul Eve (Sun,) studied this question.