london:
Lights will go out in homes across Britain today as part of commemorations marking 100 years since the outbreak of World War I, which claimed the lives of nearly one million Britons.
Millions of households are being encouraged to turn off their lights from 10 pm (2100 GMT) to 11 pm and to light a single candle, inspired by a remark by Britain's then foreign minister Edward Grey on the eve of war, "The lamps are going out all over Europe; we shall not see them lit again in our lifetime."
A single candle will be left on the steps of 10 Downing Street, the official residence of Prime Minister David Cameron as part of the campaign, organised by armed forces charity The Royal British Legion.
Cameron began a day of remembrance attending a service at Glasgow Cathedral.
"It is right to remember the extraordinary sacrifice of a generation
, and we are all indebted to them because their most enduring legacy is our liberty," Cameron told BBC News.
Representatives from around the Commonwealth honoured their fallen troops at the service in Glasgow, once the British empire's second city, where the Commonwealth Games have just ended.
Queen Elizabeth II was due to attend a commemoration at Crathie Kirk, the small Scottish church used by the royal family when holidaying at nearby Balmoral Castle.
The queen was represented at the Glasgow service by her son Prince Charles, who was later due to lay a wreath at the city's cenotaph with Cameron.
Charles's wife Camilla was to attend a service at London's Westminster Abbey, while Prince William and his wife Catherine were marking the occasion at commemorative events in Belgium.
Big Ben chimes signalled warGrey's Foreign Office declared war on Germany at 11 pm on August 4 after it rejected an ultimatum issued after the invasion of neutral Belgium.
Future war-time leader Winston Churchill described the mood in London as war was declared in his diary.
"It was 11 o'clock at night -- 12 by German time -- when the ultimatum expired," he wrote. "Along the Mall from the direction of the Palace the sound of an immense concourse singing 'God Save The King' floated in.
"On this deep wave there broke the chimes of Big Ben; and, as the first stroke of the hour boomed out, a rustle of movement swept across the room. The war telegram, 'Commence hostilities against Germany', was flashed to the ships and establishments... all over the world."
The ensuing conflict led to the death of 10 million troops and millions of civilian victims, completely reshaping the European political map.
Britain's newspapers paid tribute to the dead with special centenary editions on Monday.
The Times carried a front-page photograph of a poppy field while its editorial drew uneasy parallels between today's geopolitical climate and that which led to WWI, supposedly "the war to end all wars".
Referencing Gaza and Ukraine, the paper said: "As in 1914, there is a risk of complacency as crises swirl around us."
Other commemorative events were being held across the country while at the Tower Of London an art installation made up of hundreds of thousands of ceramic poppies -- one for each British soldier killed in the war -- poured out of the tower into the surrounding moat.
Anti-war group "No Glory in War" is also due to hold an event outside London's Houses of Parliament to remember the dead.