Before Greenwich
Until the 19th century, each British town kept local solar time. Bristol, for example, was about ten minutes behind London. With stagecoaches, such small differences did not matter much.
Railways changed that. In 1840 the Great Western Railway began using London time across its network, and by the late 1840s most British railways had adopted it. Because London time was set from the Royal Observatory at Greenwich, it became known as Greenwich Mean Time (GMT). Many towns followed the railways, though some kept their own time for years.
GMT becomes law
The Statutes (Definition of Time) Act 1880 made GMT the legal time throughout Great Britain. Ireland was given its own legal time, Dublin Mean Time. In 1884 the International Meridian Conference chose the Greenwich meridian as the world’s prime meridian, making GMT the reference for time zones worldwide. For how GMT relates to today’s atomic standard, see UTC vs GMT.
William Willett’s campaign
The idea of summer time in Britain is closely linked to William Willett, a builder from London. In 1907 he published a pamphlet, “The Waste of Daylight”, arguing that clocks should be moved forward in spring so that people would enjoy more daylight in the evenings. His plan used several small steps of 20 minutes.
Bills to introduce summer time were debated in Parliament from 1908, but none passed in his lifetime. Willett died in 1915.
The Summer Time Act 1916
World War I made the case for saving fuel. Germany and Austria-Hungary introduced summer time in April 1916, and Britain followed with the Summer Time Act 1916. The first British Summer Time (BST) began on 21 May 1916, when clocks moved one hour ahead of GMT.
What began as a wartime measure stayed. The Summer Time Act 1925 made summer time a permanent part of British life, with dates set by law.
Double Summer Time
During World War II, Britain went further. Clocks were kept one hour ahead of GMT through the winter, and in summer they moved a second hour ahead, to GMT+2. This was called British Double Summer Time (BDST). It was used in the summers of 1941 to 1945, and again in 1947, a year of severe fuel shortages after a harsh winter.
The British Standard Time experiment
From 1968 to 1971, Britain tried keeping clocks one hour ahead of GMT all year, calling it British Standard Time. Supporters pointed to lighter winter evenings, but mornings in Scotland and the north stayed dark until late. Parliament voted to end the experiment, and normal GMT winters returned from late 1971.
Today’s rules
The Summer Time Act 1972 is the basis of the current system. Over time Britain aligned its dates with the rest of Europe, and since 1996 the rule has been:
| Change | Date | Time |
|---|---|---|
| Clocks go forward to BST | Last Sunday in March | 01:00 GMT |
| Clocks go back to GMT | Last Sunday in October | 02:00 BST (01:00 GMT) |
The whole European Union changes at the same instant, so the time difference between London and Paris stays at one hour all year.
Key dates
| Year | Event |
|---|---|
| 1840 | Great Western Railway adopts London time |
| 1880 | GMT becomes legal time in Great Britain |
| 1907 | Willett publishes “The Waste of Daylight” |
| 1916 | First British Summer Time, 21 May |
| 1925 | Summer time made permanent |
| 1941–1945 | Double Summer Time in summer |
| 1968–1971 | British Standard Time experiment |
| 1972 | Summer Time Act 1972 |
The debate continues
Proposals to change British time still appear from time to time, including staying on BST all year or moving to Central European Time. Arguments usually turn on road safety, energy, and dark winter mornings in Scotland and northern England.
To see the current offset, visit the GMT page or the UK time zone guide, and check the next clock change on the daylight saving time page.