I'm looking to check the identity and authenticity of the coin in the picture. I believe it came from my wife's late grandfather. As you can see its set in a setting (of unknown metal). And I have no idea what is on the back side of the coin.

I thought I'd identified it as a half sovereign (19mm diameter). Please see link below.
https://www.bullionbypost.co.uk/gold-coins/half-sovereign/half-sovereign-victoria-old-head/
I'm not sure of its age, value, authenticity or whether or not to try and remove it from the setting. Any Advice would be great.
James x