TheUnited Kingdom usesGreenwich Mean Time (also known asWestern European Time orUTC+00:00) andBritish Summer Time (UTC+01:00) (also known asWestern European Summer Time). The latter applies between the last Sunday in March and the last Sunday in October.
Until the advent of the railways, the United Kingdom usedlocal mean time. Greenwich Mean Time was adopted first by theGreat Western Railway in 1840 and a few others followed suit in the following years. In 1847 it was adopted by theRailway Clearing House, and by almost all railway companies by the following year. It was from this initiative that the term "railway time" was derived.
It was gradually adopted for other purposes, but the legal case ofCurtis v March in 1858 held "local mean time" to be the official time.[1] On 14 May 1880, a letter signed by 'Clerk to Justices' appeared inThe Times, stating that 'Greenwich time is now kept almost throughout England, but it appears that Greenwich time is not legal time.[2][3] This was changed later in 1880, when Greenwich Mean Time was legally adopted throughout the island of Great Britain under theStatutes (Definition of Time) Act 1880 (43 & 44 Vict. c. 9). GMT was adopted on theIsle of Man on 30 March 1883,[4]Jersey in 1898, andGuernsey in 1913. Ireland adopted GMT by theTime (Ireland) Act 1916 (6 & 7 Geo. 5. c. 45), supplantingDublin Mean Time.[5]
| Summer Time Act 1916 | |
|---|---|
| Act of Parliament | |
 | |
| Long title | An Act to provide for the Time in Great Britain and Ireland being in advance of Greenwich and Dublin mean time respectively in the summer months. |
| Citation | 6 & 7 Geo. 5. c. 14 |
| Dates | |
| Royal assent | 17 May 1916 |
| Other legislation | |
| Repealed by | Statute Law Revision Act 1927 |
Status: Repealed | |
| Summer Time Act 1922 | |
|---|---|
| Act of Parliament | |
| |
| Long title | An Act to provide for the time in Great Britain, Northern Ireland, the Channel Islands, and the Isle of Man being in advance of Greenwich mean time during a certain period of the year. |
| Citation | 12 & 13 Geo. 5. c. 22 |
| Dates | |
| Royal assent | 20 July 1922 |
| Other legislation | |
| Repealed by | Summer Time Act 1972 |
Status: Repealed | |
Daylight saving time was introduced in the UK by theSummer Time Act 1916 (6 & 7 Geo. 5. c. 14), which was implemented in 1916 as GMT plus one hour and Dublin Mean Time plus one hour. The length of DST could be extended byOrder in Council, and was extended for the duration of World War I. For 1916, DST extended from 21 May to 1 October, with transitions at 02:00 standard time. On 1 October 1916, Greenwich Mean Time was introduced toIreland.[5]
At the beginning of the 20th century,Sandringham time (UTC+00:30) was used by the royal household. This practice was abolished byKing Edward VIII in an effort to reduce confusions over time.
| Summer Time Act 1947 | |
|---|---|
| Act of Parliament | |
| |
| Long title | An Act to amend the Summer Time Acts, 1922 and 1925. |
| Citation | 10 & 11 Geo. 6. c. 16 |
| Dates | |
| Royal assent | 11 March 1947 |
| Other legislation | |
| Amends |
|
| Repealed by | Summer Time Act 1972 |
Status: Repealed | |
In the summers of 1941 to 1945, during theSecond World War, Britain was two hours ahead of GMT and operating onBritish Double Summer Time (BDST). To bring this about, the clocks were not put back by an hour at the end of summer in 1940 (BST having started early, on 25 February 1940). In subsequent years, clocks continued to be advanced by one hour each spring (to BDST) and put back by an hour each autumn (to BST). On 15 July 1945, the clocks were put back by an hour, so BDST reverted to BST; the clocks were put back by an additional hour on 7 October 1945, so BST reverted to GMT for the winter of 1945.[6]
The United Kingdom experimentally adoptedCentral European Time by maintaining Summer Time throughout the year from 1968 to 1971.[7] In aHouse of Lords debate,Richard Butler, 17th Viscount Mountgarret said that the change was welcomed at the time, but the experiment was eventually halted after a debate in 1971,[8] in which the outcome might have been influenced by amajor accident on the morning of the debate.[9] Proposals to adopt CET have been raised by various politicians over the years,[7][10] including a proposal in 2011 to conduct an analysis of the costs and benefits.[11]
| Summer Time Act 1972 | |
|---|---|
| Act of Parliament | |
 | |
| Long title | An Act to consolidate the enactments relating to summer time. |
| Citation | 1972 c. 6 |
| Dates | |
| Royal assent | 10 February 1972 |
| Commencement | 10 March 1972 |
| Other legislation | |
| Repeals/revokes |
|
| Text of the Summer Time Act 1972 as in force today (including any amendments) within the United Kingdom, fromlegislation.gov.uk. | |
The dates of British Summer Time are the subject of theSummer Time Act 1972 (c. 6). From 1972 to 1980, the day following the third Saturday in March was the start of British Summer Time (unless that day was Easter Sunday, in which case BST began a week earlier), with the day following the fourth Saturday in October being the end of British Summer Time. From 1981 to 2001, the dates were set in line with various European Directives. Since 2002 the Act has specified the last Sunday in March as the start of British Summer Time with the last Sunday in October being end of British Summer Time.[12]
| Summer Time Order 1997 | |
|---|---|
| Statutory Instrument | |
| |
| Citation | SI 1997/2982 |
| Dates | |
| Made | 17 December 1997 |
| Commencement | 31 December 1997 |
| Other legislation | |
| Repeals/revokes | |
| Made under |
|
| Text of statute as originally enacted | |
TheSummer Time Order 1997 (SI 1997/2982) implemented the same start and end dates of summer time in the United Kingdom as in the European Union from 1998.[5]
A proposal to repeal European Directive 2000/84/EC and require that member states observe their own choice of time year-round was initiated in September 2018.[13] The United Kingdomleft the EU before this reform became effective; the UK is subsequently free to make its own arrangements.[14][15] As of September 2018[update], the UK Government had "no plans" to end daylight saving.[16]
In July 2019, theHouse of Lords EU Internal Market Sub-Committee launched a new inquiry into the implications for the UK of the European changes, to "explore what preparations the Government needs to make and what factors should inform the UK's response."[17]
Authority over the time zone in Northern Ireland can be legislated by theNorthern Ireland Assembly[18] but the power has never been used, asthe Republic has followed the UK. In Scotland and Wales, time zone is areserved matter, meaning that only theParliament of the United Kingdom has power to legislate.
TheIANA time zone database contains one zone for the United Kingdom in the filezone.tab, named Europe/London.
This refers to the area having theISO 3166-1 alpha-2 country code "GB". The zone names Europe/Guernsey, Europe/Isle_of_Man and Europe/Jersey exist because they have their own ISO 3166-1 alpha-2 but the zone.tab entries are links to Europe/London. There are several entries for UK possessions around the world.
Data directly fromzone.tab of theIANA time zone database. Columns marked with * are the columns from zone.tab itself.
| c.c.* | Coordinates* | TZ* | Comments* | UTC offset | UTC DST offset |
|---|---|---|---|---|---|
| GB | +513030−0000731 | Europe/London | +00:00 | +01:00 | |
| GI | +3608−00521 | Europe/Gibraltar | +01:00 | +02:00 | |
| GG | +492717−0023210 | Europe/Guernsey | +00:00 | +01:00 | |
| IM | +5409−00428 | Europe/Isle_of_Man | +00:00 | +01:00 | |
| JE | +491101−0020624 | Europe/Jersey | +00:00 | +01:00 | |
| AI | +1812−06304 | America/Anguilla | −04:00 | −04:00 | |
| MS | +1643−06213 | America/Montserrat | −04:00 | −04:00 | |
| TC | +2128−07108 | America/Grand_Turk | −05:00 | −04:00 | |
| AQ | −6734−06808 | Antarctica/Rothera | Rothera | −03:00 | −03:00 |
| BM | +3217−06446 | Atlantic/Bermuda | −04:00 | −03:00 | |
| GS | −5416−03632 | Atlantic/South_Georgia | −02:00 | −02:00 | |
| SH | −1555−00542 | Atlantic/St_Helena | +00:00 | +00:00 | |
| FK | −5142−05751 | Atlantic/Stanley | −03:00 | −03:00 | |
| IO | −0720+07225 | Indian/Chagos | +06:00 | +06:00 | |
| PN | −2504−13005 | Pacific/Pitcairn | −08:00 | −08:00 |