I’m going to revisit Birmingham as I have received a photo of the factory of James Grove and Sons in 1950.
This company was established in 1857 and ceased trading in 2012. They were one of the largest horn button manufacturers in the world. A large part of their output was uniform buttons. As well as horn, they also made casein, polyester, nylon, leather, corozo and shell buttons. The Lining Company is maintaining their web site out of historical interest. See https://jamesgroveandsons.co.uk/
New finds: Beauclaire
I’d been looking for this design, as it appears in a 1954 advertisement. It’s small, only 1 cm across the ‘base’ of the triangle. Perhaps it would have been more of a dress ornament than functional button.
From a 1954 advert.
The button below I already have in multiple colours, but not this mid-brown.