Not an easy one to pigeon-hole Chris - certainly an uncommon body shape, and smaller than usual, I'd suggest. With the handle, and the grape and vine engraving, then possibly a claret jug, but the shape isn't conforming, and although the trefoil shaped lip would suggest art nouveau (1890 - 1920 ish) again the body shape is not what you'd expect.
Possibly a table wine/claret decanter, rather than a full size example.? Assume no sign of matching Nos. on the rim/neck?
Sorry but I'm not seeing Christine's snapped pontil scar - to me it simply looks to be a case of rough grinding, but I'd agree not modern as in the last 20 years.

Certainly not Georgian as in pre 1830 - no idea as to origin - first half C20 possibly, but not sure.
Base and neck wear should be a better guide here - after all, these things were used.
I think grape and vine went on longer than you're suggesting - possibly to the middle of the C20 even.
sorry this is rather vague, let's hope someone else has a better idea.
Probably the most useful book is Andy McConnell's 'The Decanter - An Illustrated History of Glass from 1650' - 670 odd indispensable pages, but expensive.
