Western European Summer Time (WEST) is a summer daylight saving time scheme, 1 hour ahead of Coordinated Universal Time. It is used in:the Canary Islands
Portugal (including Madeira but not the Azores)
the United Kingdom
the British Crown dependencies
the Faroe Islands
Western European Summer Time is known in the countries concerned as:British Summer Time (BST) in the United Kingdom.
Irish Standard Time (IST) (Am Caighdeánach na hÉireann (ACÉ)) in Ireland. Also sometimes erroneously referred to as "Irish Summer Time" (Am Samhraidh na hÉireann).
The scheme runs from the last Sunday in March to the last Sunday in October each year. At both the start and end of the schemes, clock changes take place at 01:00 UTC. During the winter, Greenwich Mean Time (UTC+0) is used.
The start and end dates of the scheme are asymmetrical in terms of daylight hours: the vernal time of year with a similar amount of daylight to late October is mid-February, well before the start of summer time. The asymmetry reflects temperature more than the length of daylight.
Ireland observes Standard Time during the summer months and changes to UTC+0 in winter. As Ireland's winter time period begins on the last Sunday in October and finishes on the last Sunday in March, the result is the same as if it observed summer time.
Western European Summer Time Wikipedia
The following countries and territories use Western European Summer Time during the summer, between 1:00 UTC on the last Sunday of March and 1:00 UTC on the last Sunday of October.Spain
Canary Islands, regularly since 1980 (rest of Spain is CEST, i.e. UTC+2)
Kingdom of Denmark
Faroe Islands, regularly since 1981
1916–1939 summers IST
1940–1946 all year IST
1947–1968 summers IST
1968–1971 all year IST
1972– summers IST
Continental Portugal1916–1921 summers WEST
1924 summer WEST
1926–1929 summers WEST
1931–1932 summers WEST
1934–1941 summers WEST
1942–1945 summers WEST (1942–1945 midsummers WEMT=WEST+1)
1946–1966 summers WEST
1966–1976 all year WEST/CET
1977–1992 summers WEST
1992–1996 winters WEST/CET (1993–1995 summers CEST)
1996– summers WEST
Madeira, regularly since 1982
The United Kingdom
1916–1939 summers BST
1940–1945 all year BST (1941–1945 summers BDST=BST+1)
1946 summer BST
1947 summer BST (1947 midsummer BDST=BST+1)
1948–1968 summers BST
1968–1971 all year BST
1972– summers BST
In Ireland, since the Standard Time (Amendment) Act, 1971, Ireland has used UTC+1 in summer (officially "standard time", Irish: am caighdeánach, though usually called "summer time") and UTC+0 in winter (officially "winter time").
Portugal moved to Central European Time and Central European Summer Time in 1992, but reverted to Western European Time in 1996 after concluding that energy savings were small, it had a disturbing effect on children's sleeping habits as it would not get dark until 22:00 or 22:30 in summer evenings, during winter mornings the sun was still rising at 9:00, with repercussions on standards of learning and school performance, and insurance companies reported a rise in the number of accidents.
Starting in 1916, the dates for the beginning and end of BST each year were mandated by the Parliament of the United Kingdom. In February 2002, the Summer Time Order 2002 changed the dates and times to match European rules for moving to and from daylight saving time.
Note: Until 1 October 1916 time in all of Ireland was based on Dublin Mean Time, GMT − 25 minutes.