Insufficiently paid letter from Edinburgh 23 April 1952 to Reykjavik, Iceland. British 4d stamp, insufficiently prepaid, charged and stamped 'T 5C / F.S.' due. In payment for the postage due an ordinary postage stamps of 25 aur green Hekla (1948) were used in payment of the postage due, cancelled with a Reykjavik cds. Extremely rare with ordinary stamps used as postage due, even though that Iceland never issued postage due stamps.