Thanks again for those contributions - I would say that the bowl is too large for a gin glass. Balustroid or baluster is a rather loose distinction in my opinion (different people seem to call the same type of glass different things) but it is certainly one of these. The bowl is quite an early shape and size (relative to the whole glass) so 1720-30 would be reasonable, however, the colour of the metal and the presence of the many small bubbles might indicate an earlier date. The problem is that, although I have seen examples with similar metal from an early date (around 1700ish), I cannot find any examples of glasses with this particular combination of bowl, double ball knop stem and high, folded conical foot. The examples I have seen tend to have a true or inverted baluster stem, often with a tear. The high foot is, however, referred to as being found in early English glasses.
Thank you for everyone's contributions and, as stated, all ideas welcome.
Mark