Just from the top of my head I think all hammered silver coins were removed from legal tender during the reign of William III and early milled not long after 'the great re-coinage' of 1816, 1824 rings a bell. Think all copper was removed from legal tender a few years after the bronze issues of 1860. However I suspect something like Maundy issues were never removed from legal tender so there might lie the answer. Or it could be the simple answer, the 6d, 1/- and 2/6d issues of 1816.
 
	The interpretation of legal tender, even going back as early as 1970, was a lot more strictly applied, there were less alternatives to cash and fewer RM rip offs.