Big Ben was one of the brand names from the Benzon Trading Company, founded in 1922 in Denmark by Niels Benzon. This was the same company that imported the Wahl-Eversharp brand, but due to Danish import restrictions in 1933, were required to start their own domestic production. They worked with Hebborn & Co. in Heidelberg (hence, the “Big Ben / Luxor” pen, seen on this page. Luxor was one of the Hebborn brands) and also used nibs from the Peter Bock company, also in Heidelberg (for example, the Big Ben 20 on this page has a Bock nib).
It may also be interesting to note that some Danish Montblanc and Skribent pens (a sub-brand of Penol) were manufactured by Benzon.
(Some information on this page from the book “Montblanc in Denmark 1913-1992 – The Untold Story” by Claus Holten and Poul Lund.)
From left to right:
Lamy Safari (Not for sale. It’s just there for scale)
Big Ben (unknown model):
Big Ben 35: