Thanks very much for reporting back, Roobarb. It would have been Juniper Green though, not Jupiter.
I have seen a fair bit of the glass they have in Edinburgh. If it's the Museum in Chamber Street, which I think is the name of the one you mention, (it's called Chamber Street Museum by everybody who lives there) there is a fair bit of non-monart Monart there...
And engraving can be difficult to accomplish with finesse, especially if not well-practised.
But the studio never being Edinburgh Glassworks knocks HMT on the head.