London Underground (LU) was this week carrying out an urgent investigation after a runaway and defective engineering train caused chaos on the Tube network last week.
The train ran through seven stops on the northern eastern section of the Northern Line shortly before Friday morning’s rush hour before finally coming to a stop in central London.
The train first became defective at around 5.25am as it approached Archway station, travelling southbound on the High Barnet branch.
Engineers began to move the defective train northbound by coupling the unmanned carriages to an out of service Northern Line train.
But at around 6.44am the engineering train broke free heading southwards. It ran for some 13 minutes and covered around 6km before finally hitting an uphill stretch of track, bringing it to a standstill at Warren Street on the Charing Cross branch.
LU avoided disaster by diverting one passenger train onto the City branch and non-stopping a second to Kennington.
LU director Richard Parry said that safety was its “top priority”, and that it would make any conclusions and recommendations from its investigation clear.
“From the start of this incident, an immediate assessment was made and operational decisions taken to minimise the safety risk to our customers and staff,” he said.
“This horrific failure comes against a background of a systematic reduction in safety-critical jobs”
The line was suspended between Finchley Central, Archway and Camden Town to Kennington on the Charing Cross branch of the line to allow investigations to take place.
Two of these rail grinding engineering trains, comprising two power cars flanking a third car that carries the rail grinding equipment - had been in use on the Underground but LU immediately prohibited their use.
These trains were provided to LU and operated by a contractor.
The RMT rail union said it was “appalled and horrified” over the incident. It called for an immediate review of planned staff cuts.
“This horrific failure comes against a background of a systematic reduction in safety-critical jobs and safety procedures as a direct result of Transport for London’s (TfL) financial cuts programme,” it said.
“In the light of these events it is essential that TfL call a halt to their cuts plans and bring an end to the dilution of Tube safety.”
LU and the Rail Accident Investigation Branch (RAIB) are investigating. A RAIB spokesman said he could recall no similar incident in recent history.