Why do we have bst

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Last updated: April 8, 2026

Quick Answer: BST stands for British Summer Time, a daylight saving time system used in the United Kingdom from late March to late October each year. It was first introduced in 1916 during World War I to conserve energy by making better use of daylight hours. The UK switches to BST by moving clocks forward 1 hour from Greenwich Mean Time (GMT), typically on the last Sunday in March, and reverts to GMT on the last Sunday in October.

Key Facts

BST was first implemented in the UK on May 21, 1916
Clocks move forward 1 hour from GMT to BST
BST typically runs from last Sunday in March to last Sunday in October
The UK used BST continuously from 1968 to 1971 as an experiment
BST provides approximately 200 extra hours of daylight annually

Overview

British Summer Time (BST) is the daylight saving time system used in the United Kingdom, during which clocks are advanced by one hour relative to Greenwich Mean Time (GMT). The concept was first proposed by British builder William Willett in 1907, who published "The Waste of Daylight" advocating for time adjustment to extend evening daylight. BST was officially introduced during World War I through the Summer Time Act 1916, primarily to conserve fuel by reducing artificial lighting needs. The system has undergone several adjustments: from 1940-1945, Britain used "Double Summer Time" (GMT+2) during WWII; from 1968-1971, the UK experimented with year-round BST; and since 2002, EU directives have standardized the switch dates across member states. Currently, about 70 countries worldwide use some form of daylight saving time, though the UK's specific implementation remains unique to its geographical position.

How It Works

BST operates through a straightforward time adjustment mechanism: at 1:00 AM GMT on the designated spring date, clocks are moved forward to 2:00 AM BST, effectively shifting one hour of morning daylight to the evening. This creates longer evenings with natural light. The reverse occurs in autumn when clocks move back from 2:00 AM BST to 1:00 AM GMT. The specific dates are determined by EU Directive 2000/84/EC (still followed post-Brexit), which sets the switch to occur on the last Sunday in March and the last Sunday in October. The transition affects various systems: public transportation schedules adjust, electronic devices with automatic time synchronization update via network time protocols, and broadcast media announce the changes. The Royal Observatory at Greenwich serves as the official timekeeper, though most timekeeping now relies on atomic clocks coordinated through the National Physical Laboratory.

Why It Matters

BST has significant practical impacts across multiple sectors. Economically, extended evening daylight boosts retail and tourism, with studies suggesting increased consumer spending during BST months. Environmentally, reduced artificial lighting during evenings lowers energy consumption—estimates suggest savings of around 0.5% of total electricity use. For public health, additional evening daylight encourages outdoor activities, potentially reducing seasonal affective disorder. However, BST remains controversial: opponents cite disruption to sleep patterns, increased morning road accidents in darker conditions, and negative effects on agriculture and early-morning workers. The system's future is debated, with the European Parliament voting in 2019 to end seasonal time changes by 2021 (though implementation is delayed), and ongoing discussions in the UK about adopting permanent BST or reverting to year-round GMT.