SG2021ab. 1998 (3 February). Diana, Princess of Wales Commeration. 26p Multicoloured. 'IMPERFORATE STRIP OF FIVE'. Post Office fresh Unmounted mint block of ten, lower row Imperforate, upper row Imperforate to left sheet margin, partially between and at the base. David Brandon Certificate. THE UNIQUE BLOCK. Only 6 imperforate strips exist.