Back to Zulu
UK and the rest of Europe revert to 'natural' time at 0100 UTC on Sunday 29 October.
Since 1998, UK has complied with the EU directive which states that Summer - or Daylight Saving - Time will be kept between the last Sunday in March and the last Sunday in October - all changes to take place at 0100 UTC. Hence UK moves away from British Summer Time (BST), based on 15ºE (Alpha time zone), back to that based on the prime meridian (Zulu).
Clocks will return to Summer Time at 0100 UTC on Sunday 25 March 2018. In the meantime, the Winter Solstice, with the Sun at its most southerly latitude, will take place at 1624 UTC on 21 December and the Vernal Equinox, as it returns to the northern hemisphere, at 1615 UTC on 20 March 2018.
The formal conduct of international marine and air travel - and the likes of astro position-fixing - are all based throughout the year on Coordinated Universal Time (UTC - within less than a second of GMT). Alphabetical time zones are also allocated around the globe, based on 15º/1hr intervals - there are actually 25 zones due to splitting of the one around the 180ºE/W meridian. Hence UK is in 'Zulu' when using UTC, but moves to 'Alpha' during Summer Time. A Time Zone World Map from HM Nautical Almanac Office can be downloaded below.
Further details from the Royal Observatory link below . .