InterCity (or, in the earliest days, the hyphenated Inter-City) was introduced by British Rail in 1966 as a brand-name for its long-haul express passenger services (see British Rail brand names for a full history).

In 1986 the British Railways Board divided its operations into a number of sectors (“sectorisation”). The sector responsible for long-distance express trains assumed the brand-name InterCity, although many routes that were previously operated as InterCity services were assigned to other sectors (e.g., London to King’s Lynn services were transferred to the commuter sector Network SouthEast).

Info gleaned from Wikipedia