This list is for railway lines across Great Britain and Northern Ireland, which are now long abandoned, closed, dismantled, disused or mothballed.
Across the United Kingdom, examples exist of opened railways which formerly constituted cross-country main trunk lines as well as many more which served more local, or exclusively industrial, needs.
Some of the included lines have re-opened, whether in part or in full, following a period of closure, such reopenings have taken the form of independent preserved heritage railways, and of expansions to state-backed National Rail and local rapid transit & light rail networks.
Many more of these former railway lines have also been converted to cycleways, footpaths and highways.