Guinea pieces were minted from 1663 till 1817, after the sovereign had been reintroduced in 1815. It continued to be used notionally for some kinds of prices throughout the 19th century and into the 20th - for example tailors or lawyers, or for watches.

The guinea (not the coin) was in common use through the 1960s. In the late 50s/early 60s, a favourite eating place in Leicester Square was "The Guinea and the Piggy" (dreadful pun) a help-yourself buffet. You ate as much as you could for 21 shillings.

Phil