There are only three hallmarks and a maker's mark ... JB ... The soverign's head looks like George, but that lower case "a" doesn't seem to fit any years. Without a city mark, I just can't be sure. The monogram is quite clear, but somewhat naieve ... a cursive "Y" ...
Here is a pic:

(admin photo edit - please resize your pics next time)
I hope you might be able to help.
Cheers,
Randall Berger
Melbourne, Australia
.