Hi, Nell - and welcome! I've cropped & resized your photo, but I'm afraid the marks are still pretty blurry. Is there any way you can get a nice, tight shot of the marks themselves?
Hard to tell from your photograph but... if it's not a knife knife, it's very likely a letter opener or book page knife. Debora
The markings on the blade just say elkington & co as far as I can see. Can post close ups tomorrow as not able to take any right now
They used the name Elkington & Co. from 1861 to 1963, according to Wikipedia. If there are any other marks, online references should reveal more information.
Size? Maybe a dinner knife. Is the handle bone or stag? The metal design appears to be mid to late 1800s.
The way the blade is shaped (particularly as seen where it attaches to the handle) made me think it was a "knife knife" (with thanks to Debora for the term!) & not a letter opener or anything else...
Here are some closer pictures. Thanks for all the information you have given already. Do you reckon it would have been part of a set of cod have been purchased on its own?