GB Cover Postal Stationery ERROR KGV DIE 4d BLUE Used Registered Norwood ES65 RARE 1951 E335

KGV 4d DIE USED IN ERROR ON 1950s STATIONERY. Normal KGV 4d was dark green. Blue was KGVI issue colour. Seldom seen commercially used. RARE & Very Fine used. NICE FRANKING WITH KGVI Coronation issue. Please study scans to form your own opinion