Possibly a cloth seal from Jihlava, Bohemia, see BSG.CS.01466 which looks to be a parallel seal found in the Czech Republic!
From Michel Royer, "The reverse indicates a size of 63 and 3/4 (aunes)."
See BSG.CS.01466 & BSG.CS.01517 for other examples of this system, the latter with deep 'hole' dots on the horizontal lines as with this seal. See p.52, Fig.81, Oostveen, J. van, 2017, Textielloden uit de bodem van Rotterdam, for a Leiden seal with the same incised counting mark.
The find spot is evidence of Britain's cloth trade with Portugal.
