The Town and Country Planning (General Permitted Development) Order 1995

G.    Permitted development

Development by statutory undertakers for the generation, transmission or supply of electricity for the purposes of their undertaking consisting of—

(a) the installation or replacement in, on, over or under land of an electric line and the construction of shafts and tunnels and the installation or replacement of feeder or service pillars or transforming or switching stations or chambers reasonably necessary in connection with an electric line;

(b) the installation or replacement of any telecommunications line which connects any part of an electric line to any electrical plant or building, and the installation or replacement of any support for any such line;

(c) the sinking of boreholes to ascertain the nature of the subsoil and the installation of any plant or machinery reasonably necessary in connection with such boreholes;

(d) the extension or alteration of buildings on operational land;

(e) the erection on operational land of the undertaking or a building solely for the protection of plant or machinery;

(f) any other development carried out in, on, over or under the operational land of the undertaking.