There is a reference to it dated 1229 and a clear reference dated 1329.9 According to Ruding, there were over fifty mints in the reign of Edward the Confessor.
Ruding enumerates 128 mints operated at various times in the United Kingdom, including some established by usurpation, as in the reign of Stephen by certain barons, and also mints established by grants to ecclesiastics to be worked for their own profit.
5 Rogers Ruding, Annals of the Coinage, 3rd ed.
8 Ruding, op. cit.
Turning to mints in British Dominions beyond the Seas, Ruding enumerates twenty-six mints in France and Flanders used by British monarchs between 1186 and 1513, and Anglo-Hanoverian coins were struck at Clausthal, Zellerfeld and Hanover in the period 1714-1837.
2 Ruding, op. cit.