4 digit number on silver plate hallmark


I have been given what I have identified as a John Grinsell & Sons tantalus decanter. It appears it is silver plated.

It has the shield hall mark with an archer on. I can’t find what the meaning of the 4 digits are though?

It also has no key, any ideas best route to go to find one?

The number is probably just a pattern number with no external significance. For the key? Find a sympathetic locksmith.