Can't make out any of the lettering on the obverse and can't pin down whose bust.
The reverse has the emblem of the Order of the Thistle with the motto - NEMO ME IMPUNE LACESSET... "No one attacks me with impunity".
It's 25mm in diameter and weighs 6.99gms. About the size of an 18-19th century farthing/halfpenny.

Anyone have any ideas?
Identified - moved to British Coins forum - Sap