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

Year

Date

2016

27 March to 30 October

2017

26 March to 29 October

2018

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

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. 

Sunset view from Cutty Sark
Sunset view from Cutty Sark

British Summer Time and the European Union

British Summer Time (BST) changed several times over the 20th century, from double summer time during the Second World War (+ 2 hours) to continuous summer time all year round during the late 1960s (no change between 1968-1971). After much debate, a new British Summer Time Act was created in 1972 which started the tradition of changing the clocks in late March (subject to the date of Easter) and late October. Two decades later, the changing of the clocks in Britain was aligned with other European countries and from 2002 onwards, the EU stipulated that all member states should adjust their clocks on the last Sunday in March and October. Iceland is exempt from this directive, due to its northerly latitude and extreme variations in daylight and darkness throughout the year. 

Daylight saving around the world

Currently, about 70 countries worldwide adopt some form of daylight saving, mainly in Europe and North America. For countries in the equatorial regions, there is little variation in the length of daylight across the year with roughly 10-12 hours of daylight and 10-12 hours of darkness each day, so daylight saving offers no benefit. 

Interesting facts about the clock changing

Curator of the Royal Observatory, Louise Devoy, shares her favourite facts about the day the clocks change...

When the clocks first changed in 1916, there were concerns that delicate striking clocks could be damaged by people trying to force the hands back an hour. Official warnings and guidelines were printed in newspapers and magazines to reduce the number of clock ‘casualties’.

For others, changing the clocks was a well-established practice. My favourite example is King Edward VII who enjoyed hunting at his country estate in Sandringham, Norfolk. He wanted to make the most of the daylight and so in 1901, he stipulated that all clocks on the estate should run 30 minutes fast, thus creating his own ‘Sandringham Time’. It must have been very confusing for guests!

Find out more about Greenwich Mean Time (GMT)

The Royal Observatory Greenwich, home of time

Stand on the historic Meridian Line and see the ground-breaking Harrison clocks.

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