I have been in touch through the internet with a company in Italy who deal in antique Murano and modern Murano glass. They are convinced that this is Murano but the question for them was is it old or modern.
If 1935-40 the makers could be Barovier & Toso, or Fratelli Toso, or Seguso Vetri d'Arte and if a modern copy they could not be sure who would have made it.
I asked the dealers who sold it to me about it and it turns out that they had replaced the fitting on the lampbase as it was a bit shabby and taken off the chrome on the neck of the base to match the new brass fitting and rewired it to comply with todays standards.
It looks like it is 1935-40 as I can see a bit of chrome on the neck where they didn't want to go too close to the glass.
Anyway thought it might be useful for you to know my findings.