1840 2d Blue (KC/KD) MINT pair with watermark inverted. This is a key rarity of GB philately being the finest of the 2 known pairs. Stanley Gibbons sold the other one a few years ago for £150,000. I only know of one other unused example, no gum single. Stanley Gibbons catalogue price for two singles is £180,000. A magnificent showpiece accompanied by a certificate of authenticity from the Royal Philatelic Society.