May 1 1840 is the earliest known use of Britain's first adhesive stamp, a triumph for Sir Rowland Hill's 1837 proposals to reform the postal system from the arcane forms which preceded it.
However, the stamp was not created as soon as the reforms were agreed. First, the British Treasury held a competition in 1939 to find the new stamp design. However, none of the entries were considered suitable, despite 2,600 being sent in.
The design put into use - alongside the Mulready envelope - was the Penny Black, with its image of the 15 year old Victoria in profile.
Occasionally, rare competition entries have survived, and an excellent example of this is available at Spink in London next week.
With a guide price of £40,000-50,000, an anonymous entry comprising an ink drawn label (27x22mm) with truncated corners and featuring "one penny" in circular design under "V crown R" surrounded by floral motif, affixed to letter sheet marked "Multum in Parco" and "Specimen Letter".
The label at the lower left with a heavy ink stroke underneath is accompanied by the comment "This mark made by the postmaster upon the stamp will cancel it & prevent it from being used again"; the submission number "20.828/39" appears in the lower left corner.
The piece is unique and attractive - in excellent condition - and would make a good candidate for investment.
The sale takes place on May 11. We will bring you more details of the lots before then, but if you can't wait to buy a very rare, very collectible British stamp a Tyrian Plum is currently available.