Hi Nigel - good to know that you're keen on cut glass from the Stuart factory - on this forum there appears to be little interest in this particular area at the moment. Mr. Benson is the real expert on such matters - although sadly he looks in rarely these days.
Fashion is nothing if not fickle - and clear cut glass from the middle third of the C20 seems to excite few people at the moment - but as you will know, some of the Kny, Luxton, Hammond, Irene Stevens, Farquarson, Murray etc. cut glass is outstanding, although prohibitively expensive, unless you're lucky enough to find something in a charity shop.
In truth I don't know to what extent, if any, that Kny did any actual cutting - he may have been a designer pure and simple - but yes, what I'm saying is that this elongated outlined leaf was his speciality, and no doubt was a design that Stuart cutters continued to produce for some time after his departure. The overall design, where these leaves were incorporated with straight lines was a 'thirties' thing - some time before John Luxton started with Stuart, but was continued by the factory into the 1950's and probably just into the 1960's when art deco as a style ceased to be popular.
So, in my opinion yours is a 1930's design, probably based on a Kny creation, but cut 20 to 30 years later.
Of course, deco style is again popular, and remains one of the most distinctive styles in art - perhaps even more so than art nouveau. Deco epitomises modernism more than anything else - it has everything - simplicity, eroticism, clean lines, and yet remains very artistic.
What is most distinctive with your vase is the rim shape - so many vases are given a plain circular rim, whereas yours is lifted out of the ordinary.
The Miller's I mentioned is the Andy McConnell edited publication from 2006 - problem is that Miller's have knocked out so many it can be confusing to be sure of which book we're speaking. The ISBN No. is 13 978-1-845330-99-6.