The United Kingdom consists of Great Britain and Northern Ireland, and previously consisted of Great Britain and the whole of Ireland. Rail transport systems developed independently on the two island masses of Great Britain and Ireland, and most of the railway construction in the Republic of Ireland was undertaken before the creation of the Irish Free State in 1922. Thus, the logical division to discuss the history and present-day state of railways in these areas is by geographical division, rather than the nationalist division of nation states.
- Rail transport in Great Britain discusses rail transport on Great Britain, comprising England, Scotland and Wales. Here, the vast majority of the railway system standardised on the standard gauge of 4 ft 8+1⁄2 in (1,435 mm).
- Rail transport in Ireland discusses rail transport on the island of Ireland, comprising the Republic of Ireland and Northern Ireland. Here, a system using a broad gauge of 5 ft 3 in (1,600 mm) developed.
Additionally, there are rail systems in two Crown Dependencies, namely:
- Rail transport in the Isle of Man discusses rail transport on the Isle of Man, which has the largest narrow gauge railway network in the British Isles, with several historic railways (and tramways) still in operation.
- Rail transport in Alderney discusses the railway in Alderney, in the Bailiwick of Guernsey, the only working railway in the Channel Islands.
None of the British Overseas Territories have railways at present, although some, such as Bermuda were historically served by railways. Gibraltar is accessible by the Spanish and Moroccan rail systems. Hong Kong was the last dependent territory to have an extant rail system.
Similarly, for the history of rail transport, rather than the current situation (described in the above articles), see history of rail transport in Great Britain and history of rail transport in Ireland. The United Kingdom, despite its island geography, runs three separate cross border train services:
- Eurostar — Eurostar is the name of both the train operating company (TOC) and the service running passenger services from London to Paris, Brussels and Amsterdam through the Channel Tunnel.
- Enterprise — Enterprise is the name of the international joint passenger service operated between Belfast and Dublin by Northern Ireland Railways and Iarnród Éireann.
- Iarnród Éireann — Iarnród Éireann (Irish Rail) is the name of the national railway system operator of Republic of Ireland, who run a limited service between Newry via Dublin to Bray via the Northern Commuter, which operates one early morning per weekday.
- British Rail
- Great British Railways
- High-speed rail in the United Kingdom
- Inter-city rail in the United Kingdom
- Irish Sea tunnel
- Rail transport in Guernsey
- Rail transport in Jersey
- Rail transport in the Isle of Man
- Railway electrification in Great Britain
- Train overcrowding in the United Kingdom
- Transport in the United Kingdom
- Travelling Post Office
- UK Ultraspeed