The nib is an 18 carat warranted, so possibly a British-made nib for the French market. Nibs can be replaced of course, so not always a guide to the origin of the pen.
Langs named several of their pens after London locations. Did Langs ever use a box lever? (This would be a much better blog if my memory worked better.)
With the box lever and the broad cap ring it is clearly a high quality pen. I’m told that the nib is a very pleasant broad stub.
The Roman Numeral IV is on the cap top. The lever has what appears to be a castle on a hill (?), with the word WIZ over it , and a crescent moon.
Thanks to Rob Parsons for photos and information.