GB Machin SG X855 3p Ultramarine FCP 2B POTS Specimen U/M

3p Ultramarine FCP 2B (1971) POTS Specimen Post Office Training Stamp (POTS). Trimmed perfs at top. This item was part of a large estate of Machin stamps. It was originally purchased from B. Alan Ltd., a well-known dealer in the UK for 50 years. Its owner, James Skinner, was also editor of the Connoisseur Catalogue of Machin Stamps, the “go to” catalogue for decades. The collector purchased this item between 1990-2006 where it remained until 2025. Provenance in the form of the original invoice or price list from B. Allan Ltd. describing the item is provided.