Power failures caused delays and disruption on London's Tube network on Monday, as several of its busiest lines were suspended.
The Bakerloo line was completely suspended as of 1715 local time (1615 GMT), while other services including the Jubilee, Elizabeth and Piccadilly lines were facing severe or minor delays following a power outage more than two hours earlier.
Transport for London (TfL) said it was working to get the whole network back to normal service as quickly as possible.
"Due to a brief interruption of the power supply to our network, several lines lost power for a short period earlier this afternoon," TfL Chief Operating Officer Claire Mann said in a statement.
Britain's National Grid confirmed that a fault on its transmission network had caused a power failure.
"The fault was resolved within seconds and did not interrupt supply from our network, but a consequent voltage dip may have briefly affected power supplies on the low voltage distribution network in the area," a spokesperson said.
The incident also caused a small contained fire which was brought under control, National Grid said.
The potential for power failures to cause major disruption came into sharp focus in March when London's Heathrow Airport was forced to shut for 18 hours due to a fire at a nearby electrical substation, stranding hundreds of thousands of air travelers.
Transport trade union TSSA called for an inquiry into the incident to ensure a similar power outage does not happen again.
"Safety for all is key at this moment, but in due course we will need a proper inquiry into what happened and the lessons to be learned," TSSA General Secretary Maryam Eslamdoust said.
