I wrote about English-made Ingersoll pens once before, back here: http://wp.me/p17T6K-3T. That post gives some of the background to these mysterious pens.
This pen appears to have been made later, perhaps the nineteen-fifties, or maybe it’s just the superb condition that makes it appear later than it is. It has the curious mid-cap fitting for the clip, but that gives no clue as it appears from time to time from the nineteen-twenties on. The chunky section with a decided step harks back to that earlier model.
The rather splendid warranted nib is unusual. I read somewhere (can’t remember where) that some later Ingersolls were made by Wyvern. Wyvern had their own nib-making capability and may have made such a nib.
In any case, it’s an attractive and very unusual pen.
Edit: With thanks to Simon (Waudok)
This picture shows why I think Ingersoll’s were made by Wyvern. The 3 on the left are Ingersolls, the other 5 are all Wyverns. I have quite a few of this model Wyvern in these 5 colours but with different cap band configurations, and also shorter pens. I also have this model as a Kenbar (store pen for Barkers of Kensington), The City Pen from Spooners of Plymouth and some other advertising pens such as Earle’s Cement. I think I also saw one called a Regent pen on the Melbourne Pens site a few years ago.
The model names change over the years, I think the earliest is the Wyvern No 60, Clutch Selfil-Safety, Pat151753, WP Co, London (e.g. the Orange one); the Jade one is a Wyvern No 7N; and the Lapis one is a Wyvern Perfect Pen, No 81. There is also a shorter No 5, and shorter pens with an S instead of the N suffix.
The patent was applied for in 1919 (http://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&II=17&ND=3&adjacent=true&locale=en_EP&FT=D&date=19201007&CC=GB&NR=151753A&KC=A) and judging from the shape, I would have thought this pen dates to late 20s or 30s.
By the way, the section of your other Ingersoll looks like a Wyvern section to me as well.
Happy new year