18ct gold ring?

Hi I've taken some pics of a ring I have the marks are not clear in the picture but they say cp then a space and the hall mark which is a crown then 750 then and anchor on side and a capital d with a bit of a tail. The thing is i can't tell what the stone is it doesn't test as a diamond with a diamond selector 2 tester and wondered what the stone maybe. Many thanks

 

It's pretty!
If it's not testing as diamond, then other materials could be glass, rock crystal, synthetic spinel, white topaz, white sapphire, etc.
Of course, we can't tell by just your picture.
Take it to a jeweler, to find out more.

 

British 18 carat gold. So glass is less likely, white topaz, spinel, white sapphire more probable.

 

Hi thanks I've just had a look online do you think there is any chance it could be moissanite?

 

Birmingham and sounds like the 1953 D.

 

I don't think it would be moissanite.
Moissanite became popular around 1998.
And @Any Jewelry says your assay marks date to 1953, so not likely. But synthetic spinel was very popular in that period. Do have a jeweler look at it.

 

Might also be white zircons, we used those a fair bit.