Commuters faced huge delays after a power surge shut several Tube stations in central London.
Transport for London (TfL) said the electrical fault happened just after 1800 BST on Tuesday forcing them to close ten stations.
TfL said although the trains were not directly affected power was lost to systems such as escalators and CCTV.
Most stations reopened about an hour after the surge but services on many lines were running with severe delays.
TfL added that they were working with EDF Energy, who supply power to London Underground, to find out what caused the surge.