A 3d Baden-Powell pale blue on blue stamp used during the 1899-1900 siege of Mafeking is valued at £35,000-45,000 ($58,348-75,019).
The lot is to headline the sale of the Harry Birkhead collection at Spink London on March 12, which will feature philatelic items pertaining to the 1899-1902 Boer war in South Africa.
The stamp is the rare reversed design, of which only 10 examples are known to exist (three mint, seven used). Of the five used examples in circulation, this is the finest as well as having the earliest date of use.
Produced during the siege, the stamp features an image of Robert Baden-Powell, the garrison commander, who would later go on to found the Scout movement in 1907.
They are among the only stamps of the British empire not to depict the monarch.
The Mafeking Cadets Corps, forerunners of the Scouts, delivered post during the siege and were also charged with supplying and supporting the soldiers defending the town.
Another stamp from the siege, a 1/ double surcharge on a 4d green and purple-brown, carries an estimate of £7,000-8,000 ($11,699-13,336).
Thought to be a trial printing, it features an overprint of two typefaces - one serif and the other sans serif.
We have a range of rare stamps available, including this used 1882 £1 brown-lilac with a Glasgow datestamp.
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