When you place a letter in the hands of your local postal worker, you have faith that they won't take a sneak peek at your messages – but what if these well-trusted characters were secretly spies of the state? Well, that's exactly what people had to be wary of in Cromwell's England. This Long Read, written by Nadine Akkerman and Pete Langman, tells the story of a 17th-century intelligence gathering unit which deployed an array of cunning tricks to intercept and decode enemy communications.

HistoryExtra Long Reads brings you the best articles from BBC History Magazine, direct to your ears. Today’s feature originally appeared in the August 2024 issue, and has been voiced in partnership with the RNIB.

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