| Current: | BST — British Summer Time |
|---|---|
| Next Change: | GMT — Greenwich Mean Time |
| Current Offset: | UTC/GMT +1 hour |
| Difference: | 5 hours ahead of Columbus |
1917 Time Zones - London
The graph above illustrates clock changes in London during 1917.
London in GMT Time Zone
London uses Greenwich Mean Time (GMT) during standard time and British Summer Time (BST) during Daylight Saving Time (DST), or summer time.
The Difference between GMT and UTC
In practice, GMT and UTC share the same time on a clock, which can cause them to be interchanged or confused. However, there is an essential difference between the two:
- UTC is a time standard that forms the base of time zones worldwide and is not used as a time zone in any country. Time zones are defined by their offsets from UTC. Since GMT has a UTC offset of zero, there is no time difference between the two.
- GMT is a time zone used in the UK and other European and African countries.
A source of confusion is that GMT used to be the world's time standard before UTC was introduced. Until 1972, time zones were defined by their offset from GMT based on mean solar time at the prime meridian in Greenwich near London.
What About BST?
During Daylight Saving Time, clocks in the United Kingdom are set forward one hour to British Summer Time (BST). The UK is the only country that observes BST in the summer. Some other countries, such as Ireland, observe the same local time, but under a different name.
Time Changes in London Over the Years
Daylight Saving Time (DST) changes do not necessarily occur on the same date every year.
| Year | Date & Time | Abbreviation | Time Change | Offset After |
|---|---|---|---|---|
| 1900 — 1915 | No changes, UTC all of the period | |||
| 1916 | Sun, May 21 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 1 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1917 | Sun, Apr 8 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Mon, Sep 17 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1918 | Sun, Mar 24 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Mon, Sep 30 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1919 | Sun, Mar 30 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Mon, Sep 29 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1920 | Sun, Mar 28 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Mon, Oct 25 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1921 | Sun, Apr 3 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Mon, Oct 3 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1922 | Sun, Mar 26 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 8 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1923 | Sun, Apr 22 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Sep 16 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1924 | Sun, Apr 13 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Sep 21 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| * All times are local London time. | ||||
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