I've found out a bit more about these Penfold post boxes (one of eight in Cheltenham.) They were manufactured between 1866 and 1879 by the Cochrane Grove Company in Dudley. Obviously they differ from the normal round post boxes, what with them being hexagonal, but they also have a beaded edge and are topped with acanthus leaves.
I'm not the only person to become suddenly obsessed with post boxes, check out this news story.
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