You are confusing two things. A time zone (e.g. Europe/London) is a geographical region of places always sharing the same time and it does not change at a given

You are confusing two things. A time zone (e.g. Europe/London) is a geographical region of places always sharing the same time and it does not change at a given location unless time zones come and go. The zone time (e.g. GMT or BST) on the other hand is the time in use in a given time zone at a given point in time and it commonly changes twice a year between normal time and daylight saving time and back. In short, daylight saving time affects the zone time, not the time zone.