Current GMT Time

Greenwich Mean Time is commonly described as UTC+0. GMT is commonly used as a zero-offset clock. London uses British Summer Time, UTC+1, during its daylight-saving period.

#Use the location when it is available

For code and stored preferences, prefer Europe/London over an abbreviation or a bare offset. An IANA timezone carries the historical and daylight-saving rules for a region. An offset tells you only the difference from UTC at one moment.

#Convert an epoch value

A Unix timestamp is already an instant. To show it in this timezone, keep the numeric value unchanged and format it with the selected IANA name. The clock display may change; the event does not.

const date = new Date(1700000000 * 1000);

const text = new Intl.DateTimeFormat("en-US", {
  dateStyle: "medium",
  timeStyle: "medium",
  timeZone: "Europe/London",
}).format(date);

#Scheduling note

When a meeting or job is defined by local wall-clock time, store the IANA timezone with the schedule. When it is a one-time event, store the resulting UTC instant or Unix timestamp. That distinction keeps daylight-saving changes from becoming surprise reschedules.