GMT is the mean solar time at the Prime Meridian. The United Kingdom uses GMT in winter and British Summer Time in summer.
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Greenwich Mean Time originated as the civil time of the Royal Observatory in Greenwich. In everyday use it is often treated as identical to UTC, but they are not the same system: UTC is atomic, GMT is an older astronomical label. On this site, the GMT page follows Europe/London so you can see when Britain is on GMT (UTC+00:00) and when it switches to British Summer Time (UTC+01:00).
The offset shown above is computed from Europe/London at page render time using Intl.DateTimeFormat. It can change when daylight saving starts or ends.
The United Kingdom observes British Summer Time from late March to late October. During BST the London offset is UTC+01:00.
Greenwich Mean Time (GMT) uses the IANA identifier Europe/London. GMT is the mean solar time at the Prime Meridian. The United Kingdom uses GMT in winter and British Summer Time in summer.
Right now Greenwich Mean Time is UTC+01:00. The live abbreviation reported by the timezone database is GMT+1.
Daylight saving time is in effect. Standard time is labeled GMT and daylight time is labeled BST. Dates are taken from IANA data, not hardcoded on this site.
Use the converter with Europe/London as the source zone, or open the Time Zone Converter and pick a city that uses GMT. Offsets update automatically when daylight saving begins or ends.