I now have two of these, one came with a stopper, the other didn't and has no neck wear to suggest it should have had one.
What is interesting is that there is a significant difference in the top of each piece - the stoppered one is thicker and the stopper fits well, the other one is a slightly more flared top and the stopper doesn't fit it at all well, so I wondered if Morven may have been made as a carafe as well as a decanter?