Bosun Whistle - Nautical

I have a nautical whistle that my dad gave me, he said it belonged to my great grandfather, who I think had something to do with the navy. I've looked on the internet myself and it looks like its a 'bosun' whistle. The only picture I found that seemed to match my whistle was said to be Victorian on the website. My whistle is plain, with 'England' stamped in small capital letters on one side. A crown and anchor design is stamped on both sides of the whistle 'bowl'. I was wondering whether you knew how old it really was and how much it would be worth?