The London Tunnel Authority has existed, in one fashion or another, for as long as London itself, and is older even than the offices of the Royal Occultist, having existed since London was Londinium.
According to what few sources from that time remain, the first iteration of the Tunnel Authority was composed of gladiators fresh from the arenas and pressed into service as the wardens of the secrets roads running through the dark beneath the earth not long after the Roman Empire signed the Treaty of Pompelo with the Folk Below.
Currently, the Authority recruits members from the police and armed forces, as well as the occasional civilian, the latter often drafted due to unavoidable circumstances. The Royal Occultist is considered a ‘civilian advisor’ by the LTA and consulted regularly; often, the LTA have worked alongside the holder of the offices in order to stave off some dark horror, as when Aylmer Beamish, early in his career, aided the LTA in rescuing Isambard Kingdom Brunel from horrific burrowing entity of enormous size.
The Authority are responsible for the entirety of Under-London, patrolling the depths in grim rotations, twenty-four hours a day. The ghost-stations of the Underground, the semi-detached cellars, forgotten tube tracks and the sewers are their beat, and they wage an on-again, off-again cold war with the Folk Below, tracking and eliminating renegades who seek the surface.
More than once in recent years, the men of the LTA have been forced to enter some squalid East-End cellar with guns and fire and deal with what was nesting there, or wall up a long-lost tunnel in order to contain a lurking horror…