"Sources close to the talks say Tube Lines wants to do the work from 11.30pm between Sunday and Thursday for 16 months, starting next month. According to TfL, this would mean closing the line north of Stockwell from 8.30pm onwards to get trains back to depots." report The Guardian
Tube Lines said the schedule for the Northern Line upgrade was still being discussed with TfL. "We have worked very closely with London Underground to find a way of getting access to the track while producing minimum disruption to the service. It is an ongoing discussion between us," it said.
Dave Hill from the Guardian's London blog said "It's another chance for Boris to bash Gordon over the PPP. And, frankly, who can blame him?"