when the UK observes Daylight Saving Time. The name GMT comes from the Royal Observatory in Greenwich， UTC (Coordinated Universal Time) formally replaced GMT as the international standard。
creating a brief period where the gap is 4 hours. ，。
the London–New York time difference is 4 hours instead of the usual 5. The same applies in autumn: the UK falls back in late October， UTC+1) is active from late March to late October， GMT was the worlds primary time standard. In 1972， London — established as the prime meridian (0° longitude) at the 1884 International Meridian Conference. For over 80 years， UTC+0) is active from the last Sunday in October to the last Sunday in March — the winter months. BST (British Summer Time， GMT and UTC are treated as identical at UTC+0. One practical detail that catches people off guard: the UK and the US switch for Daylight Saving Time on different dates. The US springs forward in early March; the UK doesnt switch until the last Sunday in March — about 3 weeks later. During that window， London uses two timezone labels across the year. GMT (Greenwich Mean Time， maintained by atomic clocks rather than solar observation. In everyday use， the US in early November。