On Sunday, at 1am, the clocks go forward by an hour.

It's the same every year, the clocks go forward on the last Sunday of March. They go back again on the last Sunday of October.

It's 100 years since we started changing the clocks in the UK. We've mostly stuck to that routine ever since 1916 when the Summertime Act was passed.

Mostly. So what about the times when we didn't?

Daylight saving was introduced after a builder called William Willett spent years campaigning for it.

Fun fact: William Willett is the great-great grandfather of Coldplay frontman and Clocks writer Chris Martin.

BBC iWonder: Is changing the clocks a waste of time?

The first time the clocks changed in the UK was May 1916, shortly after Germany (who we were at war with at the time) put their clocks forward.

It was actually really difficult to put most clocks back an hour at the time, and the government put up posters with information on how to do it.

Double British summertime

In 1940 the clocks weren't put back at the end of summer, so we stayed an hour ahead of Greenwich Mean Time (GMT).

In spring 1941 the clocks were still put forward an hour, meaning we were TWO hours ahead of GMT.

It was the middle of World War Two, so all the extra evening daylight gave people longer to get home before the blackout.

The government also hoped it would save fuel.

Lighter evenings means darker mornings - something that can be problematic in the far northern parts of the UK.

They were eventually put back in 1947.

British Standard Time

In 1968 a similar experiment was tried. The clocks were put forward and not put back again until October 1971, keeping the UK on GMT+1 for three years.

It was called British Standard Time, presumably because calling it British Summer Time all year round seemed silly.

Nobody could really tell if it had a positive effect though, so parliament voted to get rid of it in 1970.

Several members of parliament have since tried to reintroduce British Standard Time, but none have succeeded.

When daylight saving isn't an hour

One place in the world only changes their clocks by half an hour - Lord Howe Island in Australia.

Their Lord Howe Standard Time (LHST) is 10.5 hours ahead of GMT.

The island is on Lord Howe Daylight Time (LHDT), which is GMT+11 until 3 April.

As Australia is in the southern hemisphere, Lord Howe Island put their clocks back at around the same time of year we put ours forward.

The bombing that was stopped by daylight saving

In 1999 four would-be terrorists loaded two bombs into two cars. The bombs were set to go off at 6.30pm.

Their intention was to load the bombs onto the luggage racks of two intercity buses before hopping off and driving away.

They armed the bombs in a Palestinian area. Their targets were in Israel.

Israel had turned the clocks back a day before but the bombers hadn't noticed the difference. The bombs blew up at 5.30pm local time while still in their cars, killing the bombers.

There's more about the bombings in BBC Radio 4's The Clocks Go Forward Tonight.

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