This fine miniature is on a single leaf bound into an unrelated volume at the British Library:
The BL description is here, and this leaf is mentioned briefly by François Avril, who attributes it to the illuminator who executed a copy of Le Débat du Chrétien et du Sarrasin (Paris, BnF, ms. fr. 948) written by Jean Germain, Bishop of Chalon-sur-Saône (1436-1461) (see François Avril & Nicole Reynaud, Les manuscrits à peinture en France 1440-1520, Paris, 1993, p.195).
The miniature was presumably one of a facing pair in a Missal, but the other one, presumably representing a Crucifixion, has not yet been identified.
Does anyone know its whereabouts? And leads will be gratefully received.