Vintage Sterling Silver GPO Post Office Savings Bank Book Passbook Charm

Lovely little vintage item 

I am not sure exactly when these where made - possibly 1970's ??

It opens up - but there is nothing inside

No markings - tests silver

It's a bit tarnished and a few creases / pinhead marks visible - it's also missing it's jumping but that's very easy to fix

Measures 20mm x 15mm

Unusual little item