Here you go Jon, I lifted this from the Treasure act document.
http://finds.org.uk/documents/treasure_act.pdf
all coins that contain at least 10 per cent of gold or silver by weight of
metal and that come from the same find, provided a find consists of at
least two coins with a gold or silver content of at least 10 per cent. The
coins must be at least 300 years old at the time of discovery. In the case of
finds consisting of coins that contain less than 10 per cent of gold or silver
there must be at least ten such coins; they will also need to be at least 300
years old.