| Current: | GMT — Greenwich Mean Time |
|---|---|
| Next Change: | BST — British Summer Time |
| Current Offset: | No UTC/GMT offset |
| Difference: | 4 hours ahead of Columbus |
1971 Time Zones - London
The graph above illustrates clock changes in London during 1971.
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 |
|---|---|---|---|---|
| 1970 | No changes, UTC +1 hour all of the period | |||
| 1971 | Sun, Oct 31 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC |
| 1972 | Sun, Mar 19 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 29 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1973 | Sun, Mar 18 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 28 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1974 | Sun, Mar 17 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 27 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1975 | Sun, Mar 16 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 26 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1976 | Sun, Mar 21 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 24 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1977 | Sun, Mar 20 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 23 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1978 | Sun, Mar 19 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 29 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| 1979 | Sun, Mar 18 at 2:00 am | GMT → BST | +1 hour (DST start) | UTC+1h |
| Sun, Oct 28 at 3:00 am | BST → GMT | -1 hour (DST end) | UTC | |
| * All times are local London time. | ||||
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