A pair of 1907 Nyasaland MCA stamps (2d and 4d) could make £18,000-22,000 ($23,339-28,526) in Spink's fourth part of the sale of the Lionheart Collection of British Empire stamps.
Nyasaland (modern day Malawi) was a British protectorate when the stamps were issued.
Both stamps display the Multiple Crown CA (MCA) watermark and include a large swathe of their original gum.
The auction house describes them as "an outstanding pair of these famous and very rare stamps, of which only twelve examples of each exist in private hands."
The pair could easily outstrip their estimate. Last year a near identical pair realised £22,000 ($33,130) in a sale at Spink.
An 1860 four cent British Guiana die proof is valued at £10,000-15,000 ($12,974-19,462).
The stamp was designed as a replacement for the temporary stamps issued in the 1850s.
These earlier specimens are among the rarest and most sought after in the world - in 2014 the unique 1856 1c magenta sold for a world record $9.4m.
The present lot is extremely rare and would make an excellent display piece.
Other items on offer include a 1904-1910 Malaya Straits Settlement $100.
The rare, high-denomination specimen is expected to bring in around £10,000-12,000 ($12,966-15,559).
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