According to Mr. Burt, Britain’s last electricity failure on a comparable scale occurred in 2008. That, too, was a result of two power plants going offline: Homes in London and the southeast of England lost power, and rail passengers were affected.

Although it took less than an hour for power to be restored on Friday, hundreds of passengers were stuck on stalled trains, found themselves in darkened tunnels and endured long hours waiting in crowded stations. The delays on the rail network continued into Saturday morning, as trains and staff members, displaced overnight, were unavailable in the morning.

Adding to the delays, trains faced speed restrictions across the southeast of England because of expected high winds.

On social media, people posted images of thick crowds in stations like King’s Cross in London. One user posted a photo while walking through a tunnel, having escaped a stranded train after two hours.

The event inspired some to joke about uncertainty over Brexit. “Was that #power cut someone attempting to fix Britain by turning it off and on again?” one user, Emma Clarke, wrote on Twitter.

The Times of London ran a large picture of the chancellor, Sajid Javid, who visited National Grid on Friday, hours before the power cut, with the caption “Don’t touch that dial, chancellor.”