Under the public-private partnership (PPP) imposed on the system by the Government, one thing has changed. Yesterday nothing moved on the line, but it was difficult to find an organisation to blame.
Drivers had refused to work following the failure of the emergency braking system on five trains. They said to operate the services would put passengers at risk.
Responsibility for maintaining trains - and therefore the braking system - has been farmed out to the private sector. So in this case the Tube Lines consortium would be to blame, it seemed. But, in the particular case of the Northern line, responsibility for keeping the trains going is the subject of a private finance initiative involving the engineering company Alstom. London Underground says Tube Lines is in charge of maintenance, but Tube Lines says Alstom has day-to-day responsibility.
To make matters more complicated, Tube Lines points out that London Underground is "ultimately" responsible for the safety of passengers. The consortium adds, for good measure, that the braking system was designed by London Underground.
The saga began on 9 September, when a driver stopped at a red light. There was a signalling fault, so he was told to proceed slowly. As he passed the light, the emergency braking system should have activated. It did not.
As a precautionary measure drivers were ordered to test all trains by driving them slowly through red signals. The system failed to work on three more occasions. Last Thursday London Underground ordered Alstom to check all trains on the route. But because of the checking process it was only able to supply half of the fleet last Friday, causing massive disruption.
This Wednesday an emergency braking system on a fifth train failed. London Underground decided for the first time under the PPP regime to issue an "emergency direction notice", which allows London Underground managers to direct and oversee Alstom's attempts to correct the problem.
During the course of the week four drivers were reportedly sent home for refusing to drive the trains on safety grounds. On Wednesday more colleagues declined to take services out.
A London Underground spokesman said the situation was intolerable. "It is clear that maintenance of the Northern line train fleet was not being done to the correct standards."
Even before yesterday's shutdown, the Northern line lived up to its reputation as The Misery Line. It was the only Tube route whose performance was deteriorating. Delays are more than 30 per cent worse than when the network was partly privatised.
London Assembly Liberal Democrats called for the Chancellor and Mayor to find out as a matter of urgency how the Tube maintenance contracts could be brought back in-house. The Transport spokesman, Geoff Pope, said: "The fiasco shows the PPP deal was ill-judged, ill-conceived and poorly implemented."