Mainline Rail is most standard gauge pernament way, which is that owned by:

Difficulties over definitionEdit

Although systems such as the London Metro are larger and more comprehensive in some regards than certain "mainline rail" companies, as well as sharing certain technical and operational characteristics with their heavy rail brethren, they are not considered as being part of the "mainline rail" group of companies. The difference is based on historical differences rather than technical ones, with mainline rail companies effectively descendants of the Big 8 railway companies.

To further complicate matters however, many private lines, metro and light rail routes were formerly part of the the Mainline Rail network. Examples include LakesLine (Private Company), GMAX 1 train-tram and the Epping extension of the Central line of London Metro