I say ... I don't know. The general look of it strongly indicates Moncrieff years, but is it pre- or post-war? Could be either.
I have one that I guess is from the same time as Roy's. It is shown at Row 2, Column 4
in one of my catalogue pages. It's only a smallish image and there are no other views of it as yet. It has what looks like the same green-white jasper ground as Roy's, and it does not have "dark glass" to the dome. That's one of my reasons for stating on the web page that it's 1940s/50s. However ...
... It has a snapped off pontil scar, with "crunchy bits", and that would lead many folk to think it must be 1930s. And perhaps it is, but just happens to be a "brighter" example. There is something unique (to me) about the weight, though. As well as an indented, snapped off pontil mark, it has overall smooth, but unpolished grinding to the base! Make of that what you will.
One other thing about my weight ... it was one of the first I ever bought and it was covered in scratches and marks such that the dome was extremely dull. It was only later, when I found out that it was by Paul Ysart, that I thought about getting it cleaned up, which I did (by Bob Hall) many years afterwards. When it was cleaned, I was amazed at the crispness of the colours when compared to most of my other PY "1930s" weights. And I only paid Â£20 for it in an auction in Birmingham, and I only bought it because nobody else wanted it!