WW1 On War Service 1915 official war workers badge

A scarce original First World War period official war worker's identification badge; unusual gilt brass blue enamel title surround 'On War Service 1915' with white enamel convex centre; the reverse impressed with early maker's details 'THOMAS FATTORINI BOLTON'. Good condition, complete with original buttonhole fitting, enamel with minor edge loss in the 7 o'clock position, gilt finish remains bright.Diameter approx 27mm.