A little danger here of me confusing the issue, so just to clarify the Sowerby side of things..............
In Simon Cottle's book on Sowerby, he reproduces a plate of designs from Pattern Book 30 dated December 1933, which appears to be the first list in which these unusual shaped pieces occur (this is page 4 from 1933 on the CD) - colours available are given as Flint, Amber, Green, Rosalin, and Powder Blue - described as Table Centres, and all bowls seem to be classed as design No. 2505 (although two pieces are without a design No. but I'm assuming all the same in view of the design), and each supplied with a black plinth (two separate designs). None of these has feet, and all are either simply round bases, or on a standard pedestal base.
All four variations of the bowl have eight points on the flange, and each point is separated by a smaller point. It would appear that 2505 continued in production until at least 1956, being offered in the same lists as 2583.
The four footed variation doesn't appear until page 4 in the late 1930's list, where it's described as design No. 2583 and appears for the first time that I can see - the examples shown are without a plinth. However, 2583 is to be seen sitting on plinths in subsequent lists, although visually the pairing looks clumsy and footed pieces look better without the plinth.
Presumably this heavily flanged and unusual pattern was successful - the main difference between the two is that 2583 has been re-designed to have feet, although there are other more subtle differences. Both of the Sowerby designs have an eight pointed flange, which is the most noticable difference when compared to yours Angela, since yours has 12 points.
Both 2505 and 2583 are conspicuous pieces - they look weird yet attractive, and I must have seen loads over the past few years - yesterday's being the only example I've bought though, and that only because it was uranium.
None of which helps you Angela, and hope you will forgive the rambling, but thought I needed to correct some of my earlier comments which were incorrect.
Maybe the design was so succesful that it was lifted by another factory.
If I have any of the above wrong - please say so