Yes, it’s a Chester hallmark with the date letter R for 1900. The maker’s mark is JD over WD for the Sheffield company James Deakin & Sons. I suspect that it may be the silver back of a brush from a grooming set, the holes which you mention being for the bristles.
Thank you Phil, my first attempt at dating silver worked! And yes, now I can see that it was a brush, I just wonder how it got into a field now. Amanda