Post Office GPO Round Seal?

GPO? Seal, Broad Arrow Seal, Image & Found by Bilox
Found in the Wetherby / Goldsboro / Knaresbough area, 20mm diam x 7mm thick.

Blank, traces of a rusted wire binding // crown / Broad Arrow T / 1

There is a suggestion that these are military seals for ammunition but no reference is given.