London Underground Limited, Tube Lines Limited and Schweerbau GMBH appeared at the Old Bailey following the early-morning incident in August 2010.

The court heard a broken down engineering train was being towed uphill towards Highgate tube station when a connection failed and the train broke free.

The train ran downhill out of control, southbound on the London Underground Northern Line for 16 minutes.

The train eventually came to an unaided stop caused by an uphill incline on the approach to Warren Street station, by which time it had covered over four miles, passed through seven populated stations and reached speeds of up to 30mph.

London Underground Limited, Tube lines Limited and Schweerbau GMBH all pleaded guilty to safety charges.

Ian Prosser, ORR’s Director of Safety, said: “London Underground is one of the safest railways in the world and normally has a very good safety record. The companies responsible for running and maintaining services have an important duty to ensure that their workers and members of the public are not exposed to unnecessary safety risks.

“However, in this case, London Underground, Tube Lines and Schweerbau, through inadequate management and planning, failed to ensure the safe recovery of an engineering train.

“This is clearly unacceptable, and led to a potentially catastrophic incident on the Northern Line where the train careered out of control for over four miles.

“It was only the professionalism of control room staff taking decisive action which prevented a collision between trains, and averted a much more serious outcome.

“We welcome the steps taken by the companies to improve safety management on London Underground since this incident. The regulator will continue to closely monitor the actions of all parties involved, and will not hesitate to step in should further safety failings be found.”