Broadly, in my geographical patch, and always a favourite and interest-provoking scene for me: the branches originating in pre-Grouping times with the Great Northern, and Midland, Railways never passenger-served, existing basically in the interests of ironstone extraction in the otherwise deeply-rural countryside between Melton Mowbray and Grantham.
Quite intricate rail doings involved featuring essentially two separate GNR lines, with subsidiary branches: one running southward from Belvoir Junction between Sedgebrook and Bottesford on the Grantham Nottingham route, the other setting out east / north-east / north from Scalford on the GNR / LNWR Joint line. By the 1950s, these two mini-systems had grown to be at their extremities, only a couple of miles from each other. Additionally, there was the Midlands branch from Holwell Junction at the ironworks of that name, between Melton Mowbray and Grimston on the Midlands MM Nottingham line: which ran north-eastwards, crossing over the GN / LNW Joint line (the latter in tunnel at that point) to make physical connection at Wycombe Junction, with the GNRs branch out of Scalford.
These lines though never running for passengers, and chiefly if not entirely existing for the benefit of the ironstone industry clearly counted as fully-paid-up constituents of their respective owning companies: recognised thus, by the Ian Allan Pre-Grouping Atlas & Gazetteer, and Jowetts Railway Atlas. And a one-inch Ordnance Survey map of the region, from the pre-Grouping era, handed down in our family -- shows all these ironstone lines with the OS "mineral lines, sidings, and tramways" symbol; but labels at any rate the two Great Northern lines as GNR Waltham Branch (that starting from Scalford) and GNR Woolsthorpe Branch (that starting from Belvoir Jun.).