I wanted to let you know that your question has been viewed, I will send this to Robert. He will pick this up as soon as he signs on to the site. I am going to opt out so he can do that.
Thanks for the question about the silver cigarette box.
Here's a quick answer just in case this is still active and relevant, my apologies if not.
Stylistically, the box dates to the mid-20th century and has Canadian sterling hallmarks.
Made by Henry Birks & Sons, head office, Montreal, a highly reputed canadian maker.
Auction value in the current market £100 - £140.
I do hope this helps!