Thank you for finding the piece and for pointing me to Muurla - I'd not managed to find this on my own. The piece I have is the same as that on Muurla but it is definitely in a Meri Lasi box complete with a Meri Lasi label so I wonder if both works made the same design, or if one sold the design to the other glassworks? The box on mine looks rather elderly rather than it being a brand new piece, so it's still a bit of a puzzle.
What can I say? Thank you very much. You've solved one of my mysteries - the spiral decanter which I've been pondering on the board since I bought it - and given me more info about some of the others, including one of my mother's favourites (the big blue piece you ID'ed as Florentine).
Ref Muurla and Meri, are you saying there's a connection between the two glassworks or is it that they are just both Finnish companies?
Thanks to you both for your info.