Another option would be British Railways Pre-Grouping Atlas & Gazetter
Published by Ian Allan It shows the state of the railways before the "Big Four"
I am always referring to my(second) copy,(first worn out)

There are the Midland Railway Distance Diagrams if you can get hold of them, published around 1900, but reprinted more recently.

They concentrate on the Midland in detail, but do show certain other lines even wagonways and industrial lines.