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It is quite normal to find the Leopard's Head mark on larger items assayed at Newcastle.
The reason the Leopard's Head was struck by some provincial offices, was due to a badly worded Act of Parliament. When the old standard was restored following the passing of the 1719 'Act for Laying a Duty on Wrought Plate' , Parliament seemed almost oblivious to the working of the provincial offices, and worded the Act as if it was only directed at London.
I only have to hand a shortened version of the Act to hand, and it makes no mention of any particular office. The part of the Act that caused the confusion was as follows:
From and after 1st June , 1720, all silver vessels of plate or manufactured of silver shall not be less in fineness than that of 11oz. 10dwt. of fine silver in every pound troy, or of silver less in finess than 11oz. 2dwt. of fine silver in every troy pound; which two different standards of wrought plate shall be severally and respectively marked with distinguishing mark; (that is to say), vessels made of silver plate or manufactured silver, not less in fineness that 11oz. 10dwt. of fine silver in every troy pound, to be marked with the workman's mark, the mark of the wardens of the mystery or craft of the goldsmiths, and with the figure of the lion's head erased and the figure of a woman called the Britannia; and all vessels of silver plate or manufactured silver, not less in fineness than 11oz. 2dwt. of fine silver in every pound troy, and under the degree of 11oz. 2dwt. of fine silver in every pound troy, shall be marked with the workman's mark, the wardens of the mystery or craft of the goldsmiths as aforesaid, and with the the figure of the Lion Passant, and the figure of a Leopard's Head.
Following the passing of the Act, the provincial offices had no choice really but to comply with the badly worded law, and Exeter, York, Chester, and Newcastle added the Leopard's Head to their marks. Exeter dropped that particular mark in 1777, but the others continued. Neither Birmingham or Sheffield used the mark following their establishment in 1773.