Britain’s rarest stamps? The story of Britain’s Abnormals

De la Rue’s surface printing plates wore out at more or less predictable intervals, typically after 35,000 sheets. So they made sure that replacement plates were always available. As each new plate was made, six sheets were printed on gummed, imperforate paper and submitted to Somerset House for approval. These were called ‘imprimaturs’ from the Latin word meaning ‘let it be printed’; a more accurate term would be ‘registration sheets’.

Of the six sheets, one was retained by Somerset House, while the others were perforated and distributed for circulation as normal. In most cases this went unnoticed, as the new plate was put to press soon afterwards. But in a few rare instances, something changed: a design, a colour, a watermark or postal rate. So the new plate was never used and the stamps from those five