British railway companies: Since the earliest railway sanctioned by Act of Parliament - for the Surrey Iron Railway in 1801 - the railway system in the United Kingdom has had many changes, reflected in the structure of this category. Included in the categories here are:
- Early railways: Small companies that operated the early railways (1820s to 1840s) that were later amalgamated into larger concerns.
- Pre-grouping railways: Companies that operated from 1850s to 1922 and were later grouped into the 'Big Four' companies.
- Big Four railways: From 1923-1947 the 'mainline' railway network was operated by four large railways on a regional basis.
- Joint railways: Some railways were owned and operated by a group of other companies and some survived through to 1948.
- British Railways: From 1948-1994 the 'mainline' railway network was in the hands of the single nationalised operator, British Railways (later promoted as British Rail).
- Post-privatisation companies: From 1994, a number of privately owned companies have operated and maintained 'mainline' railway track and trains.
- Minor railways: Some small railways were never considered part of the national 'mainline' network, and continued an independent existence.
- Heritage railways: Following large closures of the rail network in the 1950s-1960s, 'heritage' railways were formed to run mainly tourist services on old railway lines.