Seventeen thousand people gathered around Stonehenge on Wednesday to mark the summer solstice, cheering and beating drums as the sun rose at 04.58 BST. Daylight saving time - as summer time is known in the rest of the world - has a colourful history. First thought up by American inventor and politician Benjamin Franklin in 1784, the system is now used by more than 70 countries.

Manipulations of Greenwich mean time, however, have often been controversial. In October 1999, the King of Tonga, Taufa'ahau Tupou IV, put the clocks forward one hour, ensuring that his island would beat neighbouring Fiji to the millennium. In 2001, the Mayor of Mexico City managed to spark a constitutional crisis by arguing with the president over who had the right to decree what the time was. In September 1999, three Arab Israeli terrorists were blown up by their own bomb after misunderstanding the timers set by West Bank Palestinians. The West Bank was on daylight saving time; Israel wasn't.

Britain's timekeeping history is less turbulent, though no less complex. The Summertime Act of 1916 established two clock changes per year. During the second world war, double British summer time was invented as an energy-saving device, effectively putting the country on the same footing as mainland Europe - GMT+1 in the winter, and GMT+2 in the summer. In 1947, Britain reverted to normal.

Then, in 1968, a three-year experiment was conducted with British Standard Time, keeping the clocks fixed throughout the year on GMT+1. However, the dark winter mornings were unpopular, particularly in Scotland. In 1971, MPs voted to return to the system that endures today.

Yet the debate continues about transferring to Single/Double Summertime (SDST) - the current convoluted buzzword. Research showed an 11.7% reduction in road casualties between 1968 and 1971. An extra hour's light in the evening is thought to offer savings of up to £35m in fuel costs. Crime rates also drop with longer evenings.

SDST has had an interesting range of supporters over the years. Last October, London mayor Ken Livingstone noted its benefits for the tourist industry. In March this year, Lord Tanlaw's Lighter Evenings (Experiment) Bill was rejected despite support from the Royal Society for the Prevention of Accidents. In October 1998, Lord Archer put forward a backbencher bill that would have broken Britain up into different time zones. "I don't see why Londoners should have to suffer being in the dark at 3.30pm simply to please Scotland," he said. In the media, this debate tends to fizzle into life every October, with a number of commentators calling for the clocks to change at Hadrian's Wall and not at Calais.

"That's fine if they want to," says Fiona Hyslop, education spokesperson for the Scottish National Party. "We believe in self-determination for the English. But I wouldn't want to see Scotland change."

Elsewhere, supporters of SDST have taken matters into their own hands. Last October, Richard Kemp, general manager of the Shugborough Estate in Staffordshire, attempted to stick to summer time during the winter to encourage more visitors. "We didn't actually last that long," he says. "But it drew a lot of media attention." His move was backed by the Chamber of Commerce as well as the local MP. "Britain outside London closes down for tourists in the winter," explained Mr Kemp. "An extra hour would probably give us a 20% increase in visitors. We're going to try again this year, so watch this space."

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