Major power cut hits London and parts of England
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UK Power Networks has said: "We believe this is due to a failure to National Grid's network, which is affecting our customers."
It owns and maintains the electricity cables in southeast England, the east of England and London.
The power outage has caused widespread traffic disruption on the roads and railways.
Transport for London said that some traffic lights were not working and it advised caution on the roads.
London North Eastern Railway tweeted: "Due to a problem under investigation between #Stevenage and #KingsCross, all lines towards London are blocked.
"Train services running to and from these stations may be cancelled or delayed by up to 60 minutes."
Rail operator Thameslink said many of its trains were "at a stand". ■