Loft find!
Beautiful Antique Zither banjo.
It's a Windsor No. 4 Zither Banjo, made in Birmingham, England and though it's not dated I think probably made in 1920's.

I'm a banjo player myself and friend let me know about this one. It's got some issues, mainly aesthetic (I think some of the frets need pressing back down in places as there is a very slight fret buzz in some areas.) I would keep it myself as I enjoy playing it, the build quality is fantastic, but I have too many banjos.....

Zither banjos were designed to have a longer sustain then other banjos, this one rings very nicely. 

It's very playable, the action is nice and low.
Perfectly intonated.
Fretboard/neck shows no signs of warping.
This a very well made instrument.
from the research I've done, the neck is walnut, the board ebony and the body rosewood, head calf vellum.
There are new looking strings on it, with a wound 3rd.
Comes with orignal case - a bit scruffy but for possibly 100 years old, not too bad!

Please look at all the photos
I think it looks like a repair job has been done around the shoulder area. 
Some of the veneer from the edge of the body is peeling.

Could be a wonderful restoration project.
Restored these can fetch upwards of £500.