Sotheby's is to offer the Philatelic Collection of Lord Steinberg in a series of two London sales on September 6-8 and 21.
The unique characteristic of the Northern Irish businessman's collection is that it contains only mint blocks of four or larger multiples.
The highlight of the sale is undoubtedly lot 1118, a unique mint block of the 1927 De Pinedo Airmail 60c from Newfoundland, in modern day Canada.
Estimated at £120,000-150,000, the stamps commemorate the 1927 flight to Italy from Newfoundland by the Marchese Francesco de Pinedo, one of the leading pioneer aviators.
It ranks as the most important of all Newfoundland and world airmail blocks.
It had always been accepted that only two blocks of four survived from the issue of 300 stamps.
The other block was divided into singles, following its sale at auction over 30 years ago. This leaves the present example as the sole survivor.
Harry Dalmeny, deputy chairman of Sotheby's, said of Lord Steinberg: "In his latter years he could often be found racing from the House of Lords to stamp auctions where his fierce determination to see off other bidders meant he secured the greatest prizes in philately, before returning to vote on affairs of state."
The sales will feature 2,068 lots and the collection is estimated in the region of £4m.
Paul Fraser Collectibles will bring you further previews of the auction over the coming weeks and all the key results.
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