LONDON — Clocks across the United Kingdom went back one hour at 2am on Sunday, marking the end of British Summer Time and the return to Greenwich Mean Time for the winter months. The change gave most people an extra hour of sleep.

The twice-yearly clock change, established under the Summer Time Act and governed by European daylight-saving coordination, shifts sunrise and sunset an hour earlier. Mornings become lighter while evenings grow darker, a transition that typically coincides with the final weekend of October.

Sleep charities and road-safety groups used the occasion to issue familiar guidance. The Royal Society for the Prevention of Accidents has long warned that earlier darkness raises the risk of collisions involving pedestrians and cyclists during the evening commute, and renewed calls for improved visibility.

The change also reignited debate over whether Britain should abolish the ritual. Campaigners at organisations including the Lighter Later movement argue that permanent summer time would reduce accidents and boost wellbeing. Farming groups in Scotland have historically opposed darker winter mornings.

Smartphones, computers and most modern devices adjusted automatically overnight, though owners of analogue clocks, ovens and car dashboards were reminded to update them manually before the working week resumed.