These dishes are often hard to attribute with certainty - and even a best guess can be tricky.
The canes in the outer row are, I think, from the pre-1956 years (Ysart Brothers or earlier) but the inner canes could more likely be from the Vasart Ltd years (1956 to 1964). A check with shortwave UV light would show whether the main glass is lead-based or not. If it is lead-based, then it is Vasart Ltd / Strathearn, otherwise it will be Ysart Brothers.
I do not know of any information that helps to date these items by shape.
I suspect however that this one is probably Vasart Ltd.