An interesting fact about the Greenwich Mean Time Zone is that the location on which the zone is based, Greenwich, doesn't actually observe GMT all-year long. This is because the United Kingdom moves into British Summer Time, or BST, which begins on the last Sunday of March and runs through until the final Sunday of October each year. BST is GMT+1 or UTC+1 and was established via the Summer Time Act of 1916.
Greenwich Mean Time, which is effectively the same as Coordinated Universal Time, is observed in the United Kingdom, Republic of Ireland, Portugal, Morocco, and the Western Sahara territory of North Africa, but only during the winter time of the Northern Hemisphere. This is because, due to daylight savings systems in these countries and territories, these areas will switch to UTC+1 during the summer months, so no longer follow standard GMT time.
This time is also used in Iceland, Ivory Coast, Ghana, Guinea, the Gambia, Burkina Faso, Guinea-Bissau, Liberia, Mali, Mauritania, Senegal, Sierra Leone, Togo, the Faroe Islands, the Canary Islands of Spain, and the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha. In all of these countries and territories, GMT time is observed all year long as there are no daylight savings systems in place.
There are also two locations that only observe Greenwich Mean Time in the summer of the Northern Hemisphere. These two areas are a small part of eastern Greenland around the community of Ittoqqortoormiit, as well as the Autonomous Region of the Azores in Portugal. These areas are too far west to be included in the Greenwich Mean Time Zone throughout the entire year but move their clocks forward one hour from UTC-1 during the summer periods to effectively observe GMT or UTC.
The westernmost point in which GMT is used is on the smallest of the Canary Islands at 18°00' W, while the easternmost point can be found in the United Kingdom in the coastal town of Lowestoft, East Anglia.