Hi there! Looks like a screw cap is being used as the closure. Spring caps were replaced by modern screw caps in the late 1950s - early 1960s. Also, does the Coat of Arms on the front label indicate "By appointment to Her Majesty the Queen?" The Royal Warrant of Queen Elizabeth II (the present Queen) was obtained in 1956. This warrant and the modern screw cap both distinguish your bottle from one of Queen Victoria's which was from 1893 until 1901.
Another reference - Any chance you can see numbers on the back or reverse side of the label? Numbers such as "43-66" means the whisky was bottled in 1943. Keep in mind, this is just a rough guide. We will reach out to our contact to see if we can have your bottle narrowed down to a more exact date.