Umbrella term used by the Association of Train Operating Companies to refer to all passenger services in Britain operating under franchise to the Government - i.e. what used to be British Rail.
In London, the term "National Rail" covers a wide range of services and can be misleading as it refers to everything from GNER's intercity service from King's Cross to Scotland, to the dense inner-suburban network in south London. Frequencies of services vary widely across local National Rail services, from the half-hourly or hourly Silverlink Barking Line to a train every two minutes between Clapham Junction and Waterloo.
Transport for London are attempting to rectify this by creating a new system of branding, the Overground Network, which guarantees at least four trains per hour off-peak and whose maps show the metro-style suburban routes like a Tube map.
See also Category Rail.