I'd agree with bat20 - very similar, if not identical to S-W, although I don't know if Wedgwood did theirs in amethyst - if it is theirs then the code/model No. is RSW/10.
The W/Fs version - although made in amethyst and similar in outline shape to S-W, is generally less fat - but according to Jackson the Baxter design has a hand finished neck, which may mean theirs has a ground/polished rim - I'm not sure - I've never owned one. The Wedgwood design looks - from the books - to have a fire polished rim, but I'm only guessing here.
Jackson adds ......... "the necks (W/Fs.) were hand-finished, so they vary quite considerably in height and diameter". Unfortunately, neither Susan Tobin nor Leslie Jackson give dimensions for the pieces they show.
Think if pushed I'd plump for S-W.
P.S. Should read more carefully .................. In Tobin's Appendix 1 - page 87 - RSW/10 is described as "vase with sheared top - so I was wrong about the fire polishing. Also they were apparently made in the following colours ............ 'Clear, Blue, Amethyst, Topaz, Cranberry, Orange and White Opal. So I guess we're there with this one being S-W.