This button follows the earlier "Penitentiaries Canada" design, but lacks the lined background and inner circle. Other, very similar, versions exist marked "Lamond & Son, Montreal" with a very slightly more linear crown. Most of these buttons are simply marked "Gaunt London."
This button appears to have been used from the c.1940s through until the change of uniform in 1963 to a more civilian style that used plain plastic buttons. It then reappears in c. 1978-79 and continues in use into the very early 1980s.