Often the way a rarity is created in philately is through an attempt by a country's Post Office to destroy all the examples of a stamp which has been printed, and a few examples slip through the net.
That is exactly what happened with the 1988 13p Christmas stamp, though with a particular twist in the story. The Post Office did a highly effective job of eliminating all the examples to be sold for common use, but allowed a few to go out as part of collections.
Production was in full swing for the 13p second class stamp in the run-up to Christmas when a Scrooge-like rise in the rate to 14p was effected. Wanting to take advantage of the increased rate, the Post Office immediately changed tack to make sure that only the 14p was available.
Unfortunately for them, they had overlooked the fact that work had started on the insertion into the 1988 yearbooks of the 1988 commemorative issues, including the 1988 Christmas set containing the 13p denomination.
A certain number of these yearbooks were subsequently sold containing the 13p stamp which should not have been issued, and which are now excellent investments.
Warwick and Warwick were one of the first auction houses to report this find and auction one of these stamps. That was in August 1989 and the U.M. stamp sold for more than £3,000. Several have surfaced subsequently and it is now catalogued at £9,000 as mint.
A Royal Mail first day cover of the full set of 5 1988 Christmas stamps, including the rare 13p denomination rather than the issued 14p denomination will go under the hammer in the auction house's rare stamp sale.
The cover is postmarked at Paddington on November 15th, the official first day of issue.
This may suggest that not all of the 13p errors came from the 1988 yearbooks, as it is unlikely that a collector would have purchased a yearbook on the day of issue and immediately removed one of the sets of stamps to affix to a first day cover.
Currently 10 of these stamps have been recorded in mint condition. 1 used and 3 on first day cover. The cover bears an estimate of £3,000 and goes under the hammer on September 1 in Warwick.
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