Clocks in Britain will go back by one hour on Sunday, 30 October, bringing an end to Daylight Saving Time, otherwise known as British Summer Time.
The clocks change at 2am on the last Sunday of October, meaning there is less daylight in the evenings and more in the mornings.
During British Summer Time, where clocks were set one hour ahead from the last Sunday in March, there is more daylight in the evenings and less in the mornings.
When the clocks go back, the UK is back on Greenwich Mean Time.
What is the history behind the clock change?
British Summer Time was first established by the Summer Time Act in 1916, after a campaign by a builder called William Willett. He was reportedly irritated with the "waste" of daylight in the early mornings of summer and suggested the change in 1907, publishing a pamphlet called The Waste of Daylight.
New Zealander George Vernon Hudson, an insect specialist, first proposed the modern idea of daylight saving in 1895.
Hudson spent his leisure time collecting insects, so favoured longer daylight hours when he could do so. He presented the idea of a two-hour daylight saving shift and presented it in a paper to the Wellington Philosophical Society.
Supporters of moving the clocks backwards and forwards argue that it saves energy, promotes outdoor leisure activity in the evening in summer, and is therefore good for physical and psychological health, reduces crime and is good for business.
Royal Society for the Prevention of Accidents has argued that lighter evenings would reduce the number of accidents. In 1968 and 1971, BST was employed all year round as an experiment.
In October 1970, an analysis of road accident data published by Her Majesty's Stationery Office suggested there had been a substantial fall in the number of casualties in the evening. However, the period in which the research was taken coincided with the introduction of drink-driving legislation and the estimates were modified in 1989.
What do critics say?
Opponents say moving the clocks permanently forward by an hour would also bring the UK in line with Central European Time, which means Britain would work during the same business hours as other European cities.
Some say changing the clocks is also economically and socially disruptive. As conserving energy was originally one of the main reasons the clocks were pushed forward, studies have shown keeping BST is still beneficial. In 2007, research by the University of Cambridge found an extra daily hour of sunlight in winter could save £485m ($593.18m) each year as people are less reliant on electricity.