A fault with the national electricity network triggered a major power cut throughout parts of Hertfordshire, Bedfordshire and north London.
UK Power Networks, which is responsible for Hertfordshire's local power supply, has said that 68 postcode areas saw electricity outages after a fault at 6.40pm yesterday (Thursday, March 25).
Street lights and traffic lights switched off in St Albans, and restaurants and shops in Hatfield and Potters Bar were forced to shut.
Engineers fixed the fault within two hours.
A UK Power Networks spokesperson said: "We apologise for the disruption and inconvenience caused.
They added: "An initial fault with the national transmission network at 6.40pm resulted in a large number of faults across parts of Hertfordshire.
"We worked as quickly and safety as possible to restore customers in stages, the first within a few minutes, with all customers restored by 8.45pm."
The National Grid is responsible for the system across the UK.
A company spokesperson said that the fault would have taken place in the East of England or London regions, but that no further detail is available.
Residents shared their experiences on social media.
One Twitter user wrote: "Power cut for the whole of St Albans.
"No street lights, traffic lights. All shops and restaurants dark.
"This is... dystopian."
Another wrote: "Houses all dark between Hatfield and Welwyn Garden City."
A restauranteur said: "Our restaurant in Potters Bar, EN6 has diners sitting in the dark trying to eat."
Residents also reported mobile phone signal outages.
Thameslink and Great Northern trains were unable to call at some Hertfordshire stations during the power cut - including St Albans City and Hatfield - due to a lack of lighting.
A Thameslink and Great Northern statement read: "If you are travelling to or from one of these stations and have not begun your journey we strongly advise delaying your journey until the issue is rectified."
Full service resumed at 8.52pm.
On Twitter, UK Power Networks confirmed that the incident was not the result of hacking or foul play.
The company has said that compensation is not usually available for power cuts lasting less than 12 hours.
An online statement for businesses reads: "Power cuts occur for many different reasons and usually without warning, so we’re not liable for any loss or damage.
"Your business insurance may cover you so please check with them.
"Most insurance companies will contact us directly if they require further information."
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