hello Otis - thanks for the interesting links.
There's nothing wrong with the phrases 'Bristol green, or Bristol blue', they are correct descriptions - insofar as they have slipped into common parlance and I'm sure we all know, generally, what is being discussed - I suspect if you said 'Warrington Green' or Sunderland blue' people would fall about in mirth and be utterly confused. However, as I said earlier, these descriptions are generalized statements, and it must be understood that whilst green and blue glass was made at Bristol, the phrase now refers to the colour and not the origin. In the C18 and C19 Bristol was dynamic entry port for the U.K., and certainly the mineral smalt used by the glass houses in that area come in via this port, and gave us the Bristol blue colour that is probably more famous than the green. I don't know, but am assuming that green was derived from either iron oxide or chromium, and perhaps this also was imported via Bristol, and so it was assumed that all coloured glass was therefore made at Bristol. It's probable that only a fraction of the quantity made actually derived from that area - but some of those few do come with a famous provenance (the decorator Edkins and Jacobs the maker for example).
Bristol green seems to come in a greater range of shades than any of the other colours, and this is borne out by comments in the books regarding the difficulty of matching individual glasses when pieces are sourced from different batches.
I have much respect for Chris Elwell's attributions, and am sure he has this right.
Although these 'Bristol' colours do go back to the first quarter of the C18, I suspect that most of the pieces we see are post c.1800 (mostly the Regency period) - the genuinely early ones are very rare.
Not so sure about the Bonhams wording - is there some error with the description - could be wrong but I'm unsure that any of those are true flutes - they seem expensive, but you do get chips with them

. The central glass (Low Countries) has the cup bowl (in the U.K. often described as a mead glass) - so looks as though they are saying the two outside pieces are British?
On most wine and ale glasses the snapped pontil seems to have gone by about 1760 - 70, and thereafter we get flatter feet and ground pontil depressions - the exception being with some pub and tavern rummers and later with inexpensive moulded glasses where the scar is left untreated - BUT, for some reason I'm not aware of, the snapped pontil scar re-appears somewhere around the Regency period. This might be an indication of higher quality glasses, but that's just my opinion. I have a couple (out of about ten) with scars.
I've a feeling that I've read somewhere that if the glass is thicker, then this is an indication of period production - as modern pieces are thinner.
You'll never get attribution on these pieces, it really is a non-starter I'm sorry to say - if you can't live without a maker's name, I'd suggest you stick to C20 Studio glass

- but a varied collection of these 'Bristol' colours - green, blue, amethyst and ruby can make an attractive display, and a lot of history comes with them. Think you'd like the blue pieces, and generally these coloured pieces are good value for money, and maybe less likely to fluctuate in value than, perhaps, some of the more fashionable areas of glass collecting.
Try reading some of the books that cover drinking glasses - you might get hooked.
Anyway, your glass is a good piece, and my personal opinion is that it's probably quite a scarce design and well worth having.
Sorry, I only know Ruby Murray, not Ruby Lane

- but perhaps you're wise to be cautious.