THE RMT union is claiming that a failed engineering train which ran out of control for 6km on the Northern Line early on 13 August had a 'near miss' with a passenger train. The incident led to the closure of the Charing Cross branch for much of Friday.

Transport for London said that around 05.25 an engineering train developed a fault as it approached Archway, travelling southbound.

Engineers began to move the defective train northbound by coupling it to another train. However, at around 06.44 the engineering train became detached and started to run away.

The Charing Cross branch was cleared and closed, as the driverless train ran out of control through Camden Town. It came to a stand at Warren Street at 06.57, halted by a slight incline.

The RMT said it was "appalled and horrified" by the incident. General secretary Bob Crow warned that this "horrific failure" was due to a "systematic reduction in safety as a direct result of financial cuts".

He added: "The runaway train, which it is suspected broke loose from a failed emergency coupling as a broken down grinder unit was being pulled northwards, represents a safety failure of the highest order. We understand that a collision with a passenger service train leaving Archway was only narrowly avoided.

“The overnight works were the responsibility of TfL subsidiary Tube Lines, managed by the private company Amey, and RMT are seeking urgent answers as to whether or not third party contractors were involved in this incident – particularly as the findings from Potters Bar ruled that third party contractors should not be involved in rail maintenance works."

London Underground said an investigation was now under way by Transport for London and the Rail Accident Investigation Branch, and that it could not comment further for now. The report into the incident will be published.