Thanks Anne. It seems to be a Hofbauer design called Byrdes, but I have not yet found an exact match online.
Some investigation indicates the history of the Byrdes design is complicated.
My piece does not seem to be the high quality lead crystal produced by Hofbauer from the late 1970s to early 1980s. After the Hofbauer factory burned down in the mid-1990s a company called Amaris made the same design for 2-3 years and then Nachtmann made it too, but not to quite the same quality in lead crystal. Apparently, some time later, the Chinese made the same design in glass rather than lead crystal. I think I may have the latter incarnation! But I only paid a fiver, so I am not too put out.
Anton