Great Britain 1840 1d black Plate 8, SG2.
A very fine used four margin horizontal strip of three lettered "CD-CF", each cancelled by a black Maltese Cross.
A scarce and most attractive multiple of the world's first postage stamp in such fine condition.
GB Specialised Catalogue Reference: AS49.
The SG catalogue value for a used pair is £1,800, with singles catalogued at £475, giving a catalogue value of £2,275+.