Connie, thanks for your thoughts... I feel it's Italian rather than Murano also. The stem reminds me of the glasses which (I think it was Ivo who said) were Florence/Empoli rather than Venice/Murano.
Kev, It is made in three main parts as you say. The holder and the ball below it are perfectly clear and appear to be made from one piece of glass. There are no mould marks at all. The bottom of the clear part which is inside the coloured twisted part is a sort of pointed ovoid shape - by holding it up to a light I can see the edge of the clear glass. The twisted stem/foot and the handles are a light amethyst colour.. All the glass is very "clean" looking (this is the only way I can describe it... not dull looking at all).
Thanks to everyone for your thoughts so far. It's still a mystery, but may now be an Italian mystery. :lol: (BTW If you click the larger picture it opens a slightly larger one again - good to see more detail.)