GMT has always zero offset from UTC. During daylight saving, the UK switches to another time zone called BST, with an offset of +1h. Other countries might call their summer time zone with a different name.
UTC != GMT because the former is not a time zone but a time standard. No country uses UTC as a time zone because UTC is not a time zone. All times in the GMT time zone are numerically equal to times expressed in UTC though.
GMT doesn't exactly have BST; rather, many places that observe GMT in the winter observe BST (which is defined as GMT +1 hour) in the summer.
Google is not the arbiter of all things, but a good clue is that Googling "current time GMT" in the summer will give you the time in Britain as though DST didn't exist.
Re:Time to Dump Time Zones
by a_plastic_bag on Sunday November 06, 2016 @04:56PM
(#12887293)
GMT doesn't change throughout the year. Birtain uses GMT during winter and BST(UTC+1) during summer though.
You also can't use 'Zulu' from https://en.wikipedia.org/wiki/List_of_military_time_zones either, for that same confusion.
The problem, like with driving, is that humans are communicating the time to humans, instead of the 'smartest' humans having programmed computers how to convey time for the rest of the humans.