It was suggested recently in a comment that Stephens Leverfils and Conway Stewart pens resemble each other closely enough to have been made by the same manufacturer. It’s not so, of course. Conway Stewart made their pens in-house and Langs made those pens for Stephens who actually manufactured nothing but ink themselves.
It’s understandable that one might see a resemblance as most British-made pens of the 30s and 40s follow a pattern. In very general terms, they have a straight-sided or gently tapered barrel, a screw-on cap with a threaded clip screw holding the clip in place, a hard rubber section even if the rest of the pen is celluloid, and they are all roughly the same size. Though there are exceptions, they mostly conform to the Standard British Pen™ design. American pens of the period differ from each other much more and the products of the major manufacturers are much easier to identify at a glance – think of Sheaffer’s streamlined pens, Waterman’s ripple hard rubber, Parker’s glorious red Duofolds and Wahl-Eversharp’s rosewood hard rubber, and later, the Skyline.
So how do you tell British pens apart at a glance? Well, in many cases you can’t. You have to pick them up and have a good look at them. Langs pens and many Mentmores are quite similar. The De La Rue lever-fillers aren’t all that different. Sometimes you have to look at the writing on the barrel or the nib to be sure, bearing in mind that some reviewers install whatever and then they had to hand when replacing damaged one.
I like that many British pens of the period resemble each other quite closely. It makes you keep your perceptions of photographs or actual pens sharp. Many sellers don’t know pens all that well and they will ascribe it by the first bit of writing they see. We are the experts (or we think we are) and it’s up to us to ensure that we don’t buy a pig in a poke.