Cut to chase, there's a distinction without a difference:

According to the article:

UTC is a standard world-wide time coordinate.

UTC should always be expressed as a 24 hr clock. It is also referred to as Zulu time.

GMT is a time zone with zero offset from UTC, so GMT = UTC.

UK observes "British summer time" which is 1 hr ahead of GMT from March ?? until ??? (don't bother to click through as this is omitted)

Click though if you want these four points expressed in 10x the words.