British Double Summer Time (BDST): UTC+2 in the UK

BDST Defined: UTC+2 During UK Summers

A conference call on a July afternoon in 1942. The organiser writes "14:00 BDST". That means 2:00 PM, but two hours ahead of Greenwich Mean Time (GMT), the same offset as Central European Summer Time today.

British Double Summer Time (BDST) was a wartime time offset of UTC+2. During the periods it was in force, clocks in the United Kingdom were two hours ahead of GMT and one hour ahead of modern British Summer Time (BST, UTC+1). The country skipped forward an extra hour beyond the usual single-hour summer shift.

For comparison, modern London in July is on BST (UTC+1). Under BDST, London was on UTC+2. On the June solstice in 2026, London sunset is 21:21 BST. Under BDST, that same clock time would have shown the sun setting an hour later, pushing evening light deep past 22:00 on the clock.

Why BDST Was Introduced: WWII Fuel and Productivity

The UK first adopted daylight saving in 1916, one year after Germany, to conserve coal during World War I. By 1940, World War II had created a far more severe fuel shortage. The government needed every possible measure to cut artificial lighting in factories, offices, and homes, and to squeeze more usable daylight into the working day.

BDST achieved two things at once:

1. Extended evening daylight for factory shifts, farming, and civil defence work.
2. Reduced demand for coal-fired electricity for lighting in the late afternoon and early evening.

The logic was blunt: if workers could start their day in daylight and finish while the sun was still up, the country could burn less coal. Every tonne saved went to the war effort.

When BDST Was Used: 1941-1945 and Summer 1947

BDST did not appear overnight. The UK used a stepped approach during the war.

Winters 1940-1945: British Standard Time (UTC+1) From 25 February 1940, the UK did not revert to GMT in autumn. Instead, it stayed on British Standard Time, which was UTC+1 all winter. Clocks were one hour ahead of GMT year-round. This was itself a radical break from the pre-war pattern of GMT in winter and BST (UTC+1) in summer.

Summers 1941-1945: BDST (UTC+2) Each spring, the clocks advanced another hour. The result:

The specific dates varied by year, but the pattern was consistent: the UK lived one hour ahead of its pre-war winter time and two hours ahead in summer.

Summer 1947: BDST returns After the war, the UK returned to a normal GMT/BST cycle in 1946. But the winter of 1946-1947 was brutally cold. Coal stocks ran critically low. The government reintroduced BDST for the summer of 1947 as an emergency fuel-saving measure. That summer, clocks were again two hours ahead of GMT.

After 1947, BDST was never used again.

How BDST Affected Daily Life: Longer Evenings, Darker Mornings

The trade-off for long summer evenings was dark winter mornings. Under British Standard Time (UTC+1) in December, sunrise in London occurred well into the morning. The 1946-1947 winter, with its fuel crisis and coal shortages, meant many people started their day in pitch darkness.

In summer, the effect was dramatic. On the June solstice, London sunrise is 04:42 BST. Under BDST, sunrise was an hour later on the clock, and sunset stretched even further into the evening. For factory workers on a typical 8:00 AM to 5:00 PM shift, the entire working day fell within daylight hours. For air raid wardens and civil defence volunteers, the extra hour of evening light meant more time to prepare before blackout.

The double shift also affected the timing of national radio broadcasts, train timetables, and pub hours, though wartime licensing was already heavily restricted.

BDST vs BST Today: Could Double Summer Time Return?

Modern BST (UTC+1) puts London one hour ahead of GMT from the last Sunday of March to the last Sunday of October. In 2026, BST starts on 29 March and ends on 25 October. Today, the UK never uses UTC+2.

Campaigns for a return of double summer time surface periodically. The most prominent was the "Lighter Later" campaign, part of the 10:10 climate change group, which proposed moving the UK to UTC+1 in winter and UTC+2 in summer. Supporters argued it would reduce energy use, boost tourism, and cut road accidents in the evening. Opponents, particularly in Scotland, pointed to the winter mornings: under permanent UTC+1, sunrise in Scotland on the December solstice would be dangerously late. Children would go to school in the dark.

No government since 1947 has adopted BDST. The current arrangement, GMT in winter and BST in summer, has been stable since 1972, with the exception of the British Standard Time experiment (1968-1971) when the UK stayed on UTC+1 year-round.

For more on how today's system works, read about British Summer Time (BST) 2026 and the history of British Summer Time.

Quick reference: BDST at a glance