Briscoes became a huge presence in Australia and New Zealand and were known to have been trading in Bristol as far back as 1750 and some rumours say they were selling trade goods and shipping slaves to British colonies in the Caribbean.
However there is no proof this coin is theirs and any evidence they were counterstamping copper coin.
There were copper tokens between 1648 and 1670 and again from 1785 to about 1815 - so for a coin dated 1720 to be counterstruck seems strange. Defacing coin of the realm was a hangable offense in 18th century Britain and especially on the monarch.
It may even be trench art or a love token. Still interesting.