I’ve posted about several examples of the Golden Guinea. This may or may not be another. It’s in black chased hard rubber, the lever is chrome plated and the barrel is threaded for posting. There is no clip. The only imprint is on the cartouche, “The Guinea 21/-” the nib is warranted 14 carat gold so that doesn’t help with identification.
I would have thought that if the pen was a Golden Guinea that’s what would have been imprinted. On balance I think this is something else. Many of these black hard rubber pens with threaded barrel ends were turned out in the 20s, most unbranded. The threaded barrel was almost an indicator of an inexpensive pen, but at 21/-this pen was comparatively expensive.
The only other pen I’m aware of with a Guinea model name is The Guinea Whytwarth but I see no indication that this is it.
Thanks to Rob P. for pictures and information.