Why change the clocks, which way should they go, and whose idea was it in the first place? British Summer Time explained.

What is British Summer Time?

British Summer Time is a mechanism to make the most of increased daylight hours that occur through northern hemisphere summer, as the Earth orbits the Sun.

At 1am on the last Sunday in March, clocks skip forward by an hour.

When do the clocks go forward in 2018?

At 2am on the last Sunday in October, the clocks go back by an hour.

When do the clocks go back in 2017?

Although this change has no effect on the length of each day, sunrise and sunset each appear an hour later in the summer. This was particularly significant at the introduction of British Summer Time in the early 20th century. 

Words by Andrew Whyte, whose photo The Lost Hour was shortlisted in this year's Insight Astronomy Photographer of the Year competition

Summer time dates, 2016-2018




27 March to 30 October


26 March to 29 October


25 March to 28 October

The history of daylight saving time

The idea of summer time or daylight saving time was first suggested in a whimsical article by Benjamin Franklin in 1784, but it was first seriously proposed in in Britain in 1907 by a keen horse-rider, William Willett. Willett published his feelings in "The Waste of Daylight" - he was incensed at the 'waste' of useful daylight first thing in the morning, during summer.

The year after Willett’s death in 1915, Germany adopted daylight saving time. Not to be disadvantaged at a time of war, the UK did the same within a few weeks. Summer time was first defined in an Act of Parliament (the Summer Time Act) in 1916 that stated for a certain period during the year legal time should be one hour in advance of GMT. From 1916 up to the Second World War, clocks were put in advance of GMT by one hour from the spring to the autumn.

Within a few years of its introduction, most countries reasonably north or south of the equator had adopted Daylight Saving Time. However, it has been controversial since the day it was first proposed.

The Second World War, an exceptional time

During the Second World War, British Double Summer Time (two hours in advance of GMT) was temporarily introduced and was used for the period when, normally ordinary summer time would have been in force. During the winter, clocks were kept one hour in advance of GMT to increase productivity.

Mostly business as usual

With the war over, Britain returned to British Summer Time as before except for a brief trial between 1968 and 1971 when the clocks went forward but did not go back. The trial was deemed unsuccessful and abandoned.

The duration of British Summer Time was changed in 1998 to bring the date of the start of summer time into line with that used in the rest of the European Community.

The argument for permanent British Summer Time

Sunset view from Cutty Sark
Sunset view from Cutty Sark

Campaigners have sought a return to British Double Summer Time or a permanent British Summer Time in order to save energy and to increase the time available for leisure in the evenings. An attempt was made by backbench MPs to change BST but The Daylight Saving Bill 2010–12 was not passed by the House of Commons.

Opponents pointed out that in the north this would have social disadvantages including for instance, the problem that in the far north-west of Scotland sunrise would occur at about 10.00 in the middle of winter and over much of the north small children would have to travel to and from school in darkness. 

Daylight saving around the world

Most parts of North America and Europe, and some areas in the Middle East, observe daylight saving time. Paraguay and southern parts of Brazil observe DST but most countries in the north of South America near the equator do not.

Find out more about Greenwich Mean Time (GMT)

The Royal Observatory is open daily from 10 am

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