hello Mat - thoughts is possibly about all you're going to get - bottles were made in unbelievable profusion just about everywhere - and shape wise this is not run of the mill, it's unusual, and not easy to pigeon-hole - believe the French did something that's referred to as a 'shoulder' - quite likely not British.
Colour is possibly either turquoise or aquamarine possibly, which might suggest Bohemian or French. Date wise it's a bit of a puzzle - doesn't look to be nouveau in design, yet could well be 1850 - 1920.
Can't see from your pix if there is any wear within the neck opening - evidence of a stopper - which obviously you don't have anyway - but wondering whether this might have been a carafe rather than a stoppered decanter - although believe most carafes were made without a disc rim, so this likely to be a stoppered bottle. The disk shaped rim looks irregular which probably means lower quality.
Is there much base wear?
Let's hope others can offer better information.