Thanks both for your help.
I checked those pattern numbers, but no real match IMHO. 5517 looks like it has a lot of little "pimpels", while mine has 4 rather evenly distributed circular indentions; neither does the shape seem to fit.
Maybe it is a Strobachova piece gone wrong?
The combination of the design (which looks mid 1950s) and the colourway (which looks early 1960s) is a little strange...
And I had thought when I bought it that a quick trail through the pattern books would reveal the PN immediately
@David: did you see that I found me the "Holy Grail" (well at least to me) of Murano glass, a substantial Flavio Poli piece?