Greenwich Mean Time (GMT) is the local mean time at the Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being calculated from noon; as a consequence, it cannot be used to specify a particular time unless a context is given. The term GMT is also used as one of the names for the time zone UTC+00:00 and, in UK law, is the basis for civil time in the United Kingdom.

The Railway Clearing House (RCH) was an organisation set up to manage the allocation of revenue collected by pre-grouping railway companies for the conveyance of passengers and goods over the lines of other companies. It went on to become the major regulatory body overseeing the day-to-day running of railways in Great Britain and setting common standards for railway companies, which ensured their safety and interoperability. The RCH also produced fare structures governing many aspects of rail transport at a national level and set limits on price increases for passenger travel.