These are the wardrobe files of the English Opera Group/English Music Theatre Company, for Britten and non-Britten operas.
The files include wardrobe plots, wardrobe inventories, prop lists, cast lists, rehearsal and performance schedules, costume designs, fabric samples, measurement charts, make-up charts and correspondence.
A wardrobe plot is an actor-by-actor, scene-by-scene inventory of all the costumes in a production, with a breakdown into every separate item in each costume.