Great Britain 1966 4d British birds (Ordinary) error, SG696aeGreat Britain 1966 4d British birds (Ordinary) error, SG696ae. A superb unmounted mint with full original gum left hand marginal block of four with red omitted affecting Black Headed Gull (beak and leg) & Robin (breast). In both cases the underlay colour greenish yellow is visible instead of red. Offered with an example of the normal block for comparison purposes. A scarce QEII error. Pierron records just 30 mint blocks. An exceptional value modern