From the Wikipedia page 
National Rail is a title used by the Association of Train Operating Companies (ATOC) as a generic term to define the passenger rail services operated in Great Britain (before the adoption of the term National Rail, "Great Britain Passenger Railway" was used). ATOC is an unincorporated association whose membership consists of the passenger train companies of Great Britain which now run the passenger services previously provided by the British Railways Board (from 1965 the Board used the title British Rail). National Rail generally does not include services that do not have a BR background; this distinction is important because National Rail services share a ticketing structure and inter-availability that do not necessarily extend to other services.
The National Rail logo was introduced by ATOC in 1999, and was used on the Great Britain public timetable for the first time in the edition valid from 26 September in that year. Rules for its use are set out in the Corporate Identity Style Guidelines published by ATOC, and available on its website. The current edition is dated 2006, but there has been at least one previous version, dated 2000. The NR title is sometimes described as a "brand" but this, according to ATOC, is incorrect. The 2000 guidelines said: 'It has not been designed as a brand or identity, but to explain to rail travellers that there is a National Rail network and material carrying this descriptor covers all passenger Train Companies.'
National Rail in London
The website is