Great Britain 1929 ½d - 1½d Postal Union Congress imprimaturs, SG434/6avarGreat Britain 1929 d1d Postal Union Congress, SG434 6avar Sideways Watermark Imprimatur Set A superb unmounted mint set of imperforate imprimaturs from the 1929 Postal Union Congress, comprising three vertical pairs of the d green, 1d red, and 1d brown, each with wide 23mm gutter margin from the rare sideways watermark coil printing. Post Office fresh each with a "BPMA" handstamp on reverse. Exceptional provenance as they were released from the