Bank of England, Cyril Patrick Mahon (1925-1929), a die proof 」1, ND (1928), no serial numbers, serial number W54 601897, green and white, ornate crowned vignette of Britannia at left, value at right, reverse blank, (EPM B212 for type), extremely fine and an excessively rare heavily-engraved die proof on large-format paper with date 6-8-29 in low margin