However , by October 2007 the date for the first train entering service had been moved to January 2009 . The first train entered service on 21 July 2009 , leaving Northumberland Park depot at 23:00 and forming train 277 leaving Seven Sisters at 23:55 to Brixton . However , by October 2007 , the date for the first train entering service had slipped to January 2009 and the first train entered service on 21 July 2009 , leaving the depot at 23:00 and forming train 277 leaving at 23:55 to .