Daylight Saving Time was first introduced in the UK during World War I to conserve energy. The Summer Time Act 1916 advanced clocks by 1 hour from 21st May to 1st October.
During World War II, Britain used Double Summer Time (GMT+2) and kept clocks 1 hour ahead of GMT throughout winter to maximize working daylight hours.
The UK experimented with keeping GMT+1 year-round, but reverted due to concerns about darker mornings in northern regions.
The current system was formalized under EU directive 2000/84/EC, harmonizing clock changes across Europe. The UK continues this practice post-Brexit.
Clocks change on the last Sunday in March (BST) and October (GMT). There's ongoing debate about abolishing seasonal changes, but no legislation has passed.