Ahaa! I've just found the auction site and enlarged their image...
The auctioneers were talking utter twaddle!!
It is indeed an LER lamp! The number on the plate is the manufacturing date of 1931, and that ties in perfectly with the clearly visible stamping of "UD" - which was a common branding of the "UndergrounD" up until 1933, whereupon, lamps were then fully marked up as "LPTB"
I had a rusty LPTB lamp, complete with copper reservoir, and have since kept a nice "LT" branded one (post 1948) that has the later, slightly enlarged ruby glass lens. The older tank (and LTE burner) was of an identical pattern to the latter, so it was salvaged in order to create a complete and functioning lamp.
Finding any images of railway lamps, especially of the humble (non loco) variety from the mid 1800's period is a bit of a problem isn't it?! The only thing that I could find was a contemporary line drawing that showed some oddly positioned side lamps. The interesting point though, is that they were of a design that was (perhaps unsurprisingly?) influenced by the type usually used on horse drawn carriages!
Why wouldn't those early railway companies have simply turned to well established contractors that were already producing oil lamps in great quantities anyway?
Incidentally, we usually use the term "oil lamp" incorrectly. Early lamps usually burned a heavy type, such as "Colza", Rape Seed or even Sunflower oil, whereas the railway lamps that we are more familiar with should perhaps really be referred to as "spirit lamps"? Many Pre-grouping ones are found specifically plated or stamped for "Kerosene" or "Petroleum", though no such distinction was made on any later examples - presumably after that American stuff called "Paraffin" really caught on over here?!
Pete.