Runaway Northern Line Tube train: Charges brought
London Underground is to be prosecuted by the rail regulator over a runaway engineering train.
An engineering train ran for four miles and ploughed through six stops on the Northern Line at the start of a morning rush hour in August 2010.
As a result, a passenger train had to be diverted.
Maintenance firm Tube Lines and Scheerbau, the train's owner, are also to be prosecuted by the Office of Rail Regulation.
Transport for London (TfL) said it was "very disappointed" with the decision.
The engineering train became uncoupled as it was towed on the Northern Line near Archway station.
It ran for nearly four miles before it stopped at Warren Street, in central London.
It came to a rest because of a slight incline at the station.'Horrific'
Passenger trains were diverted to another branch of the Northern Line while the Charing Cross branch was cleared.
Bob Crow, leader of the Rail Maritime and Transport union said: "This was an horrific incident that came perilously close to a grinder colliding with a passenger train and RMT warned at the time that it was a serious mistake on the part of London Underground to downplay the potential consequences."
Mike Strzelecki, London Underground's Director of Safety, said: "This was clearly a serious incident and London Underground and Tube Lines acted quickly to investigate its causes and take action to ensure that the risk of such a rare incident recurring was minimised.
"Following the incident LU immediately put in place procedures to remove the engineering train and tow-bar from use on the railway.
"Since then LU and Tube Lines have put in place even tighter approvals and controls for the design and use of all such equipment.
"LU staff's swift actions meant that this incident was drawn to a safe conclusion."