What's it worth?

Hello all.
Just have a question here. I have a gold british half sovereign dated 1918.
It has King George IV on the obverse. For mint marks, the only thing I have found is what seems to be a small "O" on the ground under the horse on which St. George is seated on the reverse.
I was wondering if this would have any extra, numismatic value over spot.
Any help would be highly appreciated.
Just have a question here. I have a gold british half sovereign dated 1918.
It has King George IV on the obverse. For mint marks, the only thing I have found is what seems to be a small "O" on the ground under the horse on which St. George is seated on the reverse.
I was wondering if this would have any extra, numismatic value over spot.
Any help would be highly appreciated.